ok, half way through cutting. the bit broke, so i move the spindle close to me to change out the bit, but how do i tell the spindle pick up where it's left off?
thanks

As long as you have a licence then you can use Run From Here. You also want to make sure you have Safe Z setup.
To do a RFH you scroll the code to where you want to start and then press the RFH button, Mach will run through the code to that point and then a box will pop up asking you to confirm the coords and also there are a few options such as start spindle, use safe Z  and prep at feedrate. Once you have your options set and have checked the coords are correct then you can press OK. The axes will move to that position and once there you can press Start and the file will continue from there.

Just be careful the first few times you use RFH as it may not do exactly as you are expecting, best to have the feed override turned down if you are unsure.
Hood

yes. it's licenced. ok, i will try that next time. i ended up just start the whole run from the start, lucky it's a short 15 mins cut, so i have to wait just a few mins.