Just as I put one problem to bed - another pops up !

What on earth have I upset? All my Steps per Unit have gone to Hell in a Handcart..... It looks like that while I have pratting around with the Spindle Speed,I have adjusted a global setting which has altered all my Steps per Unit to something like 12 instead of 320 etc.

I have been over everthing that I think it could be, and I am cannot for the life of me find out what it can be....

There is nothing that will alter the steps per unit, only thing that would make a big difference to the motion and commanded distances would be if you set the native units to Imperial or metric.
Are your steps per unit actually changed?
Attach your xml of you want and I can have a look.
Hood

Ha.. I was just about to stumble upon that as the differences appear to be a division or multiplication of 2.54 so I think there is something in my  Test G Code trying to change the units to Imperial 

Here is my Xmas Mailing List (XML) all the same

If your code is meant to be in mm and it has a G20 at the start then it will run in inch.
Hood

Yep... Found it thanks again. As Stanley said, 'That's another fine mess you have got me out of'

The code I was running was from another Chap in the U.S. (Dur !!! )

Oh, nearly forgot, while you are there, what is meant by 'Safe Z' and are there any hard and fast rules or best practices regarding Drill/Mill usages.
Secondly where might I find a Guide as to End Mill speeds and materials?

Thanks again.

Safe Z is where the Z will raise when you ask the machine to Go To Zero via the button. It will also be used if you do a Run From Here, the prep move box will pop up and when you Ok the safe Z will be used, ie Z will raise, X and Y will move then Z will lower. I personally prefer Safe Z to be set in Machine Coords and have it just below my Max Z height. You can also have it in Work Coords or even have it an incremental value but I dont like these myself.

Not really sure what you are meaning by rules for best practice for Drill/Mill.

I usually look up the manufacturers info for the cutters I will be using.
Hood