Can't remember the equation for calculating sq footage with a Planimeter. Scale 1/8 inch = 1 foot?

Question

I designed Swimming pools for about six years. And I have been away from it long enough to forget the calculation using my planimeter. I used to take the reading from my planimeter and x it by another number to get the correct sq footage.

I again use 1/8 inch scale equalling one foot

Answer 1

Well I believe that 1/8" x 1/8" = 0.015625 in^2 = 1 ft^2 or 64 ft^2 = 1 in^2

So if you measured 15 in^2, then multiply that by 1 ft^2 / 0.015625 in^2 = 960 ft^2

Answer 2

I used to use planimeters years ago, but my instructions are at home so I do not know the factor to which you refer.  However, you can calculate your own factor by drawing a nice rectangle to your 1/8 scale and mathematically calculate the area.  Measure the same area with the planimeter a few times and average the values.  This value represents the area of the rectangle you drew.  Now just write this equation to get the constant K.

(Planimeter area)*K = known actual area

K = (known actual area)/(planimeter area)

good luck.