I have learnt M Codes and G Codes in CNC Programming. I was looking at a programming and found some statements unfamiliar to me This is how the program goes N1 T0000; G00 X0.0 Z0.0; T0101; .... ..... N2 T0000; G00 X0.0 Z0.0; M30; 1) all the programs I have studied till date number each and every line The above program doesn't do that. Is line numbering optional? 2) Line Numbers I have seen till now goes like NXXX - i.e. N005, N010 etc. The above uses N1. Is this specific syntax for a particular brand of machine? 3) What is T0000 &T0101 - I have never come across this before? The programs I have seen have a T01 in the first line - that's the only T word I have seen till now. T01 is selecting a tool T01. I don't understand why someone would select tool T0000 go to X0.0 Y0.0 & then selected T0101. i.e. What exactly was T0000 for - i.e you changed the tool after just 1 goto. 4) If N1 & N2 are line numbers, why have those 2 particular lines been numbered (as compared to other lines which haven't been labelled) Till now, I haven't actually programmed on an actual machine - just reading from books.