short range calibrater 270BN upper collimator

[farhan]

i have aproblem of measuring trunnion axis for theodolites , the T. O for calibrating theodolites tell me use upper colimator which is aboue 35 degrees up form multi target collimator (90 degrees), but actualy the upper collimator constructed at 30 degrees from the horizon as manufacturer design , so can i use continue measure trunnion axis error using upper collimator (at 30 degrees), please help me.