did anyone know that this machine required any calibaration after used for sometime ? if required, any idea how to calibrate this machine ? Thanks.
I own a 3600, too. AFAIK drop weight machines need no really calibration, but I'm not sure. Don't have the machine for a while and I'm new to stringing, so I can't tell. But you can buy a fishing scale with a hook, fix the top of the scale at the 12 o'clock support, add a piece of string around the hook and tension the string to proof if it pulls at the right tension.
Accuracy I checked mine with an 18 lb weight and pulley rig. It corresponded exactly with the scale - you can trust it.
in theory, drop weight machine works on a piece of mass and gravity, so there should not be a need for calibration. however, there is also a single point (or multiple depending on the design) of friction which is the rotating joint of the weight bar. after long use (or disuse) mechanical friction might develop. I'd suggest applying some lubrication as appropriate. checking the actual value with a digital scale doesn't hurt either.
