THE SPERRY GYRO-COMPASS 207
card and the lubber line gives the direction of the ship. The cards of gyro-compasses are marked in degrees, from 0 to 360.
A person could tell the correct time from the reading of a clock known to be five minutes fast by subtracting from the observed reading the five-minute error. He could tell the correct time without the necessity of keeping the error in mind if the clock face were rotated through 30 degrees in the clockwise direction about the spindle which carries the two hands. This procedure might not be regarded as correcting the clock error but it would at any rate make the clock indicate the correct time. In a similar manner the meridian-steaming error and the latitude error of the Sperry gyro-compass are allowed for automatically by a shift of the lubber line.
The total deviation of the gyro-axle from the meridian due to the meridian-steaming error together with the latitude error is (119 and 129):