I have had many people ask me for more information on the servo tester. This is a small device available from micron radio systems, see AeroModeller for address info. This device is used by radio flyers to test the travel of their servos.
This device is supplied in kit form and is easily assembled with the use of a small soldering iron, the kit comes with a small black box which can be discarded, after assembly of the printed circuit board and testing the PCB is enclosed in heat shrink tube, the 47k varible pot is also not required and is to be replaced by a 47K Linear slider pot which you mount on the control handle, this pot then connects across the two control lines down to the bellcrank and then onto the two connection points on the PCB, the standard servo lead is used to connect to the BEC output from the speed controller. I have obtained my 47K slider pots from EBay but you can use other electronic supplies. See attached photos of device.