Laser On TC can be a negative value.
Laser Off TC cannot be a negative value. According to the EZCad manual, laser off TC does not allow negative values, so neither did @LightBurn when he wrote the code.
In the video, Alex is using EZCAD3 and I don’t know why EzCad3 offers negative values there. In this EZCAD3 manual, Laser Off TC also doesn’t support negative values. Someone asked in the comments how he is doing that and Alex hasn’t responded.
More discussion here: TC Parameters don't seem to do anything in my Galvo laser? - #8 by Aaron.F