Hello Patrick,
Latest version is 1.0.6. To change the name of the model, you should click in the orange "Model" label. A short click allow to change the name, a long click allow to delete the model, BUT only if there are more than one model defined.
You are correct in the two first distances, but not on the 3th one. In the case you have a defined location to place the lead (say that you want to screw the lead in the firewall), then you should measure the distance from the mains (center of the scales) to the firewall. The CG Meter will calculate the exact weight of lead needed at this point to have the plane in balance. If the plane is tail heavy so the location of the lead will be behind the CG, then you should enter distance in negative numbers.
In the case you are planning the installation of the ancillaries in the model, moving bateries around, etc, to look to the best weight distribution to reduce the lead to a minimum, then it is not necessary to enter this distance, the plane will be in balance when the reading be zero.
Gaspar