The 71-3220 K&E Coincidence Striding Level is used to establish a level line of sight with any instrument having an A.I.A. Standard 2.2498" diameter barrel- such as Brunson, K&E, Cubic Precision, Taylor Hobson, Hilger Watts, and Davidson Optronics telescopes. Sensitivity is 20 sec. Per 2mm of movement. The coincidence bubble gives you an image of both ends of the bubble...when the ends meet up- you are level!. Calibration is available at extra cost upon request and is done by a NIST certified Lab offsite. Please allow 2-3 weeks for Calibration.