Hi,
Mach3 has only one probe input.
You could dedicate another spare input as another probe signal but it will be too slow.
The current (one and only) probe input is a real-time input. Thus Mach decelerates/stops the Z axis within a few usec of receiving
a probe signal ie very quickly or 'realtime'. A normal input would be signaled back to Mach from your motion controller
(either parallel port OR external controller) but it will take up 10-12 msec. Mach would then have to issue a decelerate/stop
command to the Z axis and therefore another delay of 10-20 msec. The total delay could be anywhere up to 40 msec.
If you probed very VERY slowly you could do that without to much inaccuracy. At normal probe speeds the probe
would seriously overrun the contact point and risk smashing the probe or workpiece and even if that didn't happen the
overrun would screw your accuracy.
Mach4 has four independent probe inputs, g31, g31.1, g31.2, g31.3. Mach3 has one, g31.
Craig