Compensator for Silva 70P and 100P/PT compasses. It is recommended for use when the deviation is greater than 5 degrees when the compass is in the normal mounting position. If the deviation is less than 5 degrees, just create a deviation table.the compensator eliminates or at least limits the errors that iron or other sources of magnetic interference can have on the compass.when compensating, the boat should be in an area that is not affected by permanent or electromagnetic interference.