This might be long but I repair electro-mechanical devices for 40 yrs.Rm young makes some good weather instruments but this is the first try at a calibration unit, 18801 with 5 mins I found there weak point $1200.00 back when this was new? First off everything works it’s all there.However the two weak points is using 4xAA Batteries to drive motor, lopes unstable the transformer is the way to drive it. Forget the batteries the other is the motor clapping system, they used red lock tight on the 6/32 screw the nut that recessed in the housing spins as you rotate the thumb nut. You can’t control the clamping force as a free wheeling nut bolt, so I fig out a small clamp anywhere on the motor will allow perfect pressure, so between using the wall transformer and a 3 inch c-clamp this unit will last a long time, has a castle drive, and a rubber tube for other models, I just purchased it last week calibrated and 05103 to a 04503-P that was setup for low speed AQ 05305 it did the RPM=MPH perfect.I didn’t include the clamp due to the fact there’s smaller options for $5.00 it don’t take much to get the right force, if I had to say anything they was done right is the guide, and control is easy to change speed, it does take a few secs to stabilize, there’s a you-T video on same process only he’s has 18802 same hardware