# Land Surveyors United

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# how do i calculate the INSF?

Hi guys

Can anyone help me with this attached pic

A formula for it or any information would be appreciated

Kind Regards

Mat

This Content Originally Published by a land surveyor to Land Surveyors United Network

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### Replies to This Discussion

I amnot 100% sure of the abbreviation LNSF or INSF. The lower case is ambiguous to my eye.

When I look at the form in total, I am leaning toward a meaning of Linear Scale Facor as a percentage of length and as a resulting distance calclated from it.

Again, interpreting this form, I believe the scale factor is a characteristic of the projection and your location within it.

JAC

In sf would be instrument scale factor. This would probably come from the manufacturer of the instrument used (?).
I don't know if this will help or not but I believe that the abbreviation Delta INSF means change in scale factor. I'm not sure why one of the units would be in parts per million and the other would be in meters. In algebraic expressions, the Delta symbol almost always indicates change or difference.

I assume the previous replies are correct. Using an electronic total station - one may be invited to enter temperature, barometric pressure and relative humidity. When that is entered the display shows a scale factor for the EDM.

I believe the form is laid out in such a way that one figures the scale factor as a percentage. Then the user multiplies the raw length by the scale factor to determine the linear quantity result of applying the SF. The linear quantity is added to (or subtracted from) the raw quantity to determine the final, useful quantity.

JAC

Computed distance/measured distance

RIGHT ON

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