What does the mysterious constant marked by C on a slide rule indicate?
up vote
56
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Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
|
show 6 more comments
up vote
56
down vote
favorite
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
|
show 6 more comments
up vote
56
down vote
favorite
up vote
56
down vote
favorite
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited Nov 30 at 14:22
muru
1337
edited Nov 30 at 14:22
muru
1337
edited Nov 30 at 14:22
muru
1337
1337
asked Nov 30 at 2:56
timtfj
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked Nov 30 at 2:56
timtfj
426212
asked Nov 30 at 2:56
timtfj
426212
426212
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
timtfj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
|
show 6 more comments
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
@shoover - good one!
– davidbak
Nov 30 at 19:29
|
show 6 more comments
1 Answer
1
active
oldest
votes
up vote
66
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.6k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
66
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.6k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
add a comment |
up vote
66
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.6k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
add a comment |
up vote
66
down vote
accepted
up vote
66
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.6k352130
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.6k352130
answered Nov 30 at 3:10
TonyK
40.6k352130
answered Nov 30 at 3:10
TonyK
40.6k352130
answered Nov 30 at 3:10
TonyK
40.6k352130
40.6k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
add a comment |
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
2 days ago
add a comment |
timtfj is a new contributor. Be nice, and check out our Code of Conduct.
timtfj is a new contributor. Be nice, and check out our Code of Conduct.
timtfj is a new contributor. Be nice, and check out our Code of Conduct.
timtfj is a new contributor. Be nice, and check out our Code of Conduct.
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Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29