The 'free play' in the cables is basically how much you can pick up on the cable sheath at the carb end without causing the inner cable to pull on the throttle lever on the carb. As the inner part of the cable can "stretch", and folks have different cable setups on the R65 (79-80 bikes had (2) individual throttle cables all the way to the handlebar, while the 81-84 bikes had a single cable at the handlebar, going to a "splitter", with short separate cables for each carb coming out of the splitter. As these are all different and have different tolerances/wear, it is simplest to make all adjustments at the carb reference for cable slack. So, your cable adjust screw position may or may not be the same as mine, depending on cable type/setup, but the slack should be similar for good operation.
BMW constantly tweaked the size of the idle and main jets and needles over the years (not to mention the possibility of someone prior to you in the bike's history tweaking things further). So, the air/mixture screw positions may also be different between (2) different R65s, though they shouldn't be super different. Hence why we usually say start out at 1/2 to 2/3 of a turn from all the way in to begin with, and tweak from there - some jet/needle/airfilter setups may need to be closer to 1 whole turn, while another might be 1/2 a turn, and both be correct for the setup of each respective R65.
A rotameter is just the technical term for what the CarbTune and similar devices is - it is a vacuum gauge that uses steel slides inside of tubes instead of a fluid like mercury or ATF fluid/oil in the tubes like in a manometer. I like the CarbTune/rotameter because it cannot leak/spill and works in 2 scales/modes depending on whether it is held up one way or inverted.
