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Gauge Marks
Descriptions and values as located on the scales

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Note: Thanks to Steve Seale Ph.D. who compiled this list of the most commonly found gauge marks.
Nomenclature used here is consistent with that used in, "Pocket Book of the Gauge Marks", Panagiotis Venetsianos, The Oughtred Society, Roseville CA,, 2nd edition, 2011, 147 pp. Gauge marks in the table below are arranged in increasing order of their value

Gauge Mark Value Definition Comments
ρ or M 1.019 X 103 mils to Radians conversion
Cu
1.124 X 10-1
finding weight of Cu solid
s
1.273
4/π
Flying Fish rules; finding area of circle
C
1.128
sqrt(4/π)
used to calculate circle areas and cylinder volumes
m
1.28
used in US Gallon and meter conversions
NP or dB
1.151
Ln(10)/20
Neper/decibel conversions
'' or // or :
1182 X 104
(60*(180/π))²
used to find sines or tangents of small angles
N
1.340
used in converting British HP to/from kW
DNM
1.359
Power conversion between Imperial and Metric units
y
1.4
used in yard conversions
Cu
.1482
sqrt((.01722 X 4)/π)
finding resistance of Copper wire
Cu or Cu1
.1493
sqrt((.0175 X 4)/π)
finding resistance of Copper wire
Cu1
.1495
sqrt((0.01755 X 4)/π)
finding resistance of Copper wire
ρg
1.571
π/2
F or f
.1592
1/(2π)
for solving electrical circuit problems
cm
16
Used in cm/inch conversions
'
1.667 X 10-2
1 minute = 1°/60
converts minutes to radians
1.732
√3
Used in solving 3-φ problems
Q or ρ or ρ0 or 1°
1745 X 10-5
π/180
used to find sines or tangents of small angles
ρCu
1.750 X 10-2
finding resistance of Copper wire
d
1.772
sqrt(π)
Cu
1.785 X 10-2
finding resistance of a Copper wire
v or ρ
1.910
6/π
finding volume of sphere
Al1 or Al
.1922
sqrt((.029 X 4)/π)
finding resistance of Aluminum wire
2g
19.62
Twice the gravitational constant
' or / or ·
1970 X 10²
60*(180/π
used to find sines or tangents of small angles
R1
1.986
Molecular Gas Constant in CGS units
ρ'' or '' or S or R'' or Q''
2063 X 10²
(180*60*60)/π
used to find sines and tangents of small angles
c
2.154
∛10
used for finding cube roots when rule has no K scale
V0 or VM or MV
22.42
litrs/mol ideal gas
ideal gas calculations
1n or L or U or 1/M
2.303
1/Log10e
Used for converting between natural and common logs
kg
245
Used in lb/kg conversions
f
2.533 X 10-2
1/(4 X π
Resonant frequency calculations
F or 1F
26.8
Faraday Constant
γAl
2.700
finding weight of Aluminum wire
e
2.718
Euler number; a constant
Base of Natural Logarithms
''
2.778 X 10-4
1 second = 1°/3600
converts seconds to radians
℧ or V or 1/R
28.70
finding the voltage drop in Copper wires
ρAl
2.900 X 10-2
finding resistance of Aluminum wire
' or 1/ρ'
2.908 X 10-4
π/(180 X 60)
finding sines of small amgles expressed in minutes
W
3.027 x 10-3
finding wt. of Cu wire given dia. and length
V
30.49
23.950 X 4/π
finding voltage drop in Cu conductors
π
3.142
Ratio of circumference to diameter of a circle
3.162
√10
M
.3183
reciprocal of π
gE or g
32.19
Gravitational Constant
W
3.318 X 105
sqrt((4 X 44 X 106)/(π X 3 X 555))
finding weight of Copper wire
ρ' or ' or m or R' or Q'
3438
(180*60)/π
used to find sines and tangents of small angles
Al
35.0
finding the resistance of Aluminum wire
C1 or C'
3.568
sqrt(40/π)
used to calculate circle areas
K
.3592
273/760
gas volume calculations
1/e
.3679
Reciprocal of e
Cu
.3782
sqrt(4/(π X 8.9))
for weight calculations of round Copper wire
Cu2
.3784
sqrt(4/(π X 8.89))
for weight calculations of round Copper wire
39.4
.3937
1/(2.54)
used in in/cm conversions
J
4.186
No. of Joules in a calorie, or Watts in a calorie/sec
V
4.189
(4 X π)/3
finding volume of a sphere; usually on K scale
M
4.27 X 10²
427 Kg-M = 1 Kcal
M
.4343
Log10e
4.429
sqrt(2g) or sqrt(2 X 9.81)
used in hydraulic problems
N
.4492
1.2505 x (273/760)
ideal gas calculations
c2
4.642
∛100
used for finding cube roots when rule has no K scale
kW
465
Coupled Mark for kilowatt conversions
'' or 1/ρ''
4.848 X 10-6
π/(180 X 60 X 60)
finding sines of small angles expressed in seconds
XM
.5235
for computing reduction to the meridian
V
.5236
π/6
finding volume of a sphere
2F
53.58
2 X Faraday Constant
lbs
54
Used in lb/avoirdupois conversions
R
552.8
sqrt(40/π X 24000)
finding resistance of Copper wire
Cu
57.1
finding the resistance of Copper wire
Qo or ρ0 or ρ or R or r or U or Ro
5.730 X 101
180/π
used to find sines and tangents of small angles; to convert Degrees to Radians
60°
.5774
tan of 30° or 1/(sqrt(3))
used for 1/(sqrt(3)) or 3φ current calclations
R2
62.36
Molecular Gas Constant
in
63
Used in in/cm conversions
PS
632
Coupled mark for metric horsepower conversions
Q,, or ρ,, or ρ or ρ, or ρg
6366 X 10²
(200*100*100)/π
used to find sines and tangents of small angles
Al2
.6880
sqrt(4/(π X 2.69))
weight calculations of round Aluminum wire
N
.7136
sqrt((.4 X 4)/π)
finding resistance in Nickelin wire
PS or MOT
.7358
1 metric horsepower = .73575 kilowatt
converting horsepower to kilowatts
M
.738
Probably finding resistance in Manganin wire
E or e
775
conveting Watts to HP
HP or W
.7456
1 British horsepower = .7456 kilowatt
converting horsepower to kilowatts
A or S
.7854
π/4
calculates area of circle from diameter
K
.798
Probably finding resistance in Constantan wire
3F
80.4
3 X Faraday Constant
R3
8.205 X 10-2
Molecular Gas Constant in ISO units
dB
8.686
20/Ln(10)
Neper/decibel conversion
γCu
8.900
finding the weight of Copper wire
Y
0.9144
# meters/yard
for meters/yards conversion
gF
9.81
Gravitational Constant
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