The formula option allows you to correct a variety of problems that cannot be anticipated in advance. It does this by allowing you to enter a formula that will be used on the data items you select. The formula has two terms, a multiplier and an offset. Every item that is processed by the formula is multiplied by the multiplier and then added to the offset. The formula looks like this: I = (I * M) + O. Since the internal format for all Compass survey data is in feet and degrees, the formula operates on the data in feet and degrees no matter how the data is displayed. Keep this in mind when you are designing a formula.
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Multiplier. The multiplier can be used to correct data by a certain percentage. For example, if you have a tape measure that stretches 10% too long, you could correct the error using a multiplier of 0.9. You can also use it convert the data from an unusual measuring system. For example, you could convert yards to feet by using a multiplier of 0.3333333. If you don't want the multiplier to have any effect, set its value to one.
Offset. The offset can be used to correct bias problems. For example, if you have a compass with a five degree offset, you can correct the problem using an offset of -5. You can also use the offset to correct unusual magnetic disturbances around the cave. For instance, if part of a survey runs under a powerline, you'd have a problem that would not be easily corrected with the normal declination settings. You could fix this type of problem with an offset of same size and opposite sign as the disturbance. For example, if the disturbance changes the compass by +2.5 degrees, you could fix the problem with an offset of -2.5 degrees. If you don't want the offset to have any affect, set its value to zero.