ah, it looks like the imonitor is connected to guard and its a front panel thing.
but it says nothing about using it for guard shields. perhaps with a 250uA FS mod, it might make sense. Tempted to try bigger resistors there too see how low the full scale can go (i.e. 90k ohm)
at 100V it seems like it almost makes sense to have a guard capability. Like if you connect the guard to another prototype PCB's guard. Then the guard might even be useful, even if the cable is not the source of leakage, so its a good capability to have.