Fig. 65.
As soon as he receives the travel reference-number he will set the string accordingly, using the scale for the observing interval used.
To determine correction.—As soon as the approximate range is received, the computer sets the ruler for the range and the index at zero; he then slides the trammel to the left until the pointer is opposite the atmosphere curve as indicated by the pointers e, f, g, etc., holding the bar in place with the left hand. He then slides the bar until the pointer is at normal for atmosphere; this completes the correction for atmosphere.
He then proceeds in the same manner for wind and tide, always sliding the trammel until the pointer is at the indicated curve, holding the bar in place with the left hand and then sliding the bar until the pointer is at normal.
If the muzzle velocity is normal, no correction is made for velocity. If, however, the muzzle velocity is not normal, he makes a correction for muzzle velocity in a similar manner as for other data.
The above corrections are made before the travel is received. The computer clamps the bar and then waits until he receives the travel.
As soon as the travel is received, he sets the string, slides trammel until the pointer is opposite the string, unclamps the bar and moves it until the pointer is opposite the normal; this adds the correction for travel during the time of flight.
He then notes the total travel during the observing interval, which is indicated by the position of the string on the travel-scale corresponding to the observing interval used. He slides the trammel so that the pointer will be at the vertical line corresponding to the total travel during the observing interval, and then slides the bar to the normal; this adds the travel during the observing interval. He now clamps the bar. The register now indicates the total correction to be applied to the arm.