MACH 3 2010 Screenset Zeroing Macros

[Washout]

Hi All,
.
Couple of good things today - got my newly milled z-axis installed and working, fettled some potential stalling out of the y-axis whilst reassembling, gained about 30mm in z travel due to the old outer z plate being too long and also got hold of a "renishaw" style probing tool and wired that up.
.
Question for those (probably Jazz as normal ;-) ), who have the MACH 2010 screenset: what does the middle button do on the zeroing screen (has a + in it). I suspect it may be a block centre find but I'm a little nervous in case I crash my probe.
.
Reason I ask is I have used the other buttons that probe for the edges of a block and I can work out the centre of the block from the -/+ X and Y's and have also used the corner probing and this was very handy for re-zeroing when flipping blocks over for 2 sided machining. Method I have been using is to home and zero the machine and axis then do the edge probing which gives me the centre of the block from absolute machine cords (the spreadsheet I have been using to store the edge coords and calc the centre is attached in case it is useful). Then I go to the calculated middle of the block and zero the axis there and start my jobs for that face.
.
Oh and one other question - where can I find a macro/plug in for MACH3 to try some scanning with my probe?
.
Thanks in advance as always.
.
.
Chris