In the software revision 2, the bargraphs can be displayed in square. You can choose the display as follow: at the power on, if the potentiometer 4 is turned on the left (min value), the bargraphs are displayed on stack but if this potentiometer is turned on the right (max value) , the  bargraphs are displayed on a square. No other changes in the software or in the schematic. Download the ServoTester-4Channels-Vcc-Rev2.zip software.

Software revision 1
You can find on the internet many servo tester schematics allowing to test a single servo. This allows to check that the servo you just bought is working properly. The tester presented here allows to test a more complex set.

I developed this tester because the drone I built has a sometimes erratic operation. I had to diagnose it to understand the cause. The flight tests sometimes had an unpleasant smell of burned Electronic Speed Control (ESC) with scorched copper varnish ...

Five parameters are thus to be supervised: the length of the 4 impulses of commands (thrust, roll, pitch and yaw), and the supply voltage.

In the case of a complex realization, as for example the development of a flight controller (of drone or other) or any mixer of impulses, this tester allows to see the result of this mixer.

This tester measures pulses 1 to 2 milliseconds every 20 ms.
In the following, the term "servo" can be replaced by ESC or any other device recognizing the 1 to 2 millisecond pulses.

The supply voltage of this tester must be between 6 and 12 Vdc.

Refer to the file Super-Testeur de servos-ARTICLE.pdf. It shows the 5 possible configurations of use to check the flight controler operation.