The 76-RH190 is the undisputed "workhorse" of optical alignment. The versatile Brunson 76-RH190 transit combines the traditional main telescope with a fixed-focus cross telescope mounted in the horizontal axis of the instrument. This second telescope is fixed at infinity focus to make collimation or autocollimation with another instrument or a mirror quick and easy.(This info from Brunson) Please NOTE: $100.00 re-calibration fee added to first rental invoice.