Straight edge and machinists square

[NordicCnc]

Hello. Do you guys know what kind of straight edge and square would be good to buy? I will need those for my DIY cnc machine build. I've done some research and found the DIN874 and DIN875 standards, but I am not sure what to look for. Any help is appreciated!

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[JAZZCNC]

DIN874 is the degree of flatness and relates to the high and low points of steel rule(straight edge).
DIN875 is the degree of squareness for set squares.

There are 4 grades in each class 00, 0, 1, 2 with 00 being the best and eye-watering prices in some cases. Thou often these are only available in shorter lengths of usually 1mtr for straight edges. As they get longer the accuracy gets lower. All tolerances are measured in Um's.

If you do a google you'll find charts for each Din class with the tolerances for different lengths and sizes etc.