Product Manual

Example:
Planimeter used: Model 30; Scale ratio : 1" = 660 feet; Long Arm Extension used;
Results to be expressed in Acres.
Sc
2
x u
The formula for determination of the Acre Constant : C
A
= ------------------- ;
43560
660
2
x 0.02
Subsequently C
A
= ------------------- = 0.2 Acres ;
43560
Example:
Planimeter used: Model L20M; Scale ratio = 1: 5500; Results needed in sq. meters.
All metric scale ratios are expressed in proportional ratios. 1:5500 means that 1cm =
5500 cm. Since the result must be expressed in sq.m, we need to convert the scale
ratio accordingly: i.e. 1cm = 5500 cm or 1cm = 55m;
Therefore C
A
= 55
2
x 0.1 = 302.5 m
2
; ( 0.1 is the u-value for model 20M)
Important
Please keep in mind, that all values used in computing C
A
must be of the same unit
value, i.e. if results are needed in mile
2
, a foot scale ratio must first be converted into a
mile ratio. etc.
If your scale ratio is an architectural ratio, please check below.
Architectural Scale Ratios
like 1/32" = 1 ' or 3/4 " = 1' must be converted into an Engineering Ratio Sc
before they can be used to determine C
A
.
1/32" = 1' converts to 1" = 32'
1/16" = 1' converts to 1" = 16'
1/8" = 1' converts to 1" = 8'
Special Scale Ratios
In some instances, ( when measuring cross sections, etc.) it is possible, that the
horizontal scale is different from the vertical scale.
The basic C
A
formula is slightly altered to : C
A
= (h x v) x u ;
where h is the horizontal and v the vertical scale.
Example
h : 1"= 40' and v : 1"=20'. u = 0.01; Therefore C
A
= 40 x 20 x 0.01 = 8 ft
2
;
Please note: You find the u-value entered into the formula in your Calibration Re-
cords. The u-value shown here was extracted from the example records on the
previous page. However your u-values may be different .
3/8" = 1 ' converts to 1" = 2.666'
1/2" = 1' converts to 1" = 2'
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