Gyro Calibration

[gnirts]

Instructions contained within gyro.h gave a procedure for adjusting the GYRO_CAL_FACTOR from the default value of 1 (1000/1000) to a value that more accurately reflects the characteristics of your gyro.

Two things:

1. I accidentally spun the gyro toward -1800 instead of +1800. I thought this would not make a difference if the percent error is still the same but apparently is does. What should GYRO_CAL_FACTOR be if instead of receiving -1800 as the actual value I got -1864? If you look at the code the math behind seems to make a GYRO_CAL_FACTOR of 1036/1000 detrimental to accuracy.
2. How often do I need to repeat this procedure? Once every week or so? The instrument used to spin the gyro exactly a certain number of degrees weighs about 90 pounds and doesn't stay within easy access of the school. This also means I will not be able to repeat the calibration unless we bring this hunk of metal to the regional competition.

Thanks in advance,
Robinson

[Quick Secondary Question (sorry): does setting a digital output high mean setting it to 254, 255, or 1?]