Calibration question

[[Da...]]

This is one of the results charts from our recent calibration. I'm a bit confused, why do the limit lines (red) get further apart as the length increases? The machines tolerance is on the chart, and the tolerance STARTS at that value (.7), but then expands to almost 1.6 at the 400 mark. I like to fully understand things, and this doesn't make sense to me. 😕

[[Mi...]]

Because the accuracy of the machine is expressed as a value per length.

Eg.
0.7mm per 100mm..

The longer the distance the more inaccuracy is allowed.

[[Da...]]

But the accuracy is expressed as 0.7+L/400. and the charts limit lines are at 1.6 at the 400 mark.

[[Ri...]]

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The accuracy statement is 0.7 +L/400 where L=length in mm. The "400" is a length factor constant. It is a variable accuracy statement. 0.7 is your base accuracy (or zero length). When you want to calculate your machine accuracy you just need to know the length that you measured - in your case 420mm is the max distance on the gage. You take the 420 divide it by 400 for 1.05µm - then you add the base accuracy of 0.7µm for a total accuracy of 1.75µm.

Please note that this tolerance is a ± tolerance, so you total tolerance is ±1.75µm or ±0.00175mm.

[[Ke...]]

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[[Da...]]

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Ok, understood. The TOLERANCE is 1.75, So the green line shows what the results for the machine actually checked. The MON number off to the left is the max error over all the lengths. (0.4) The machine in Y axis at mid, mid, mid checks W/I 0.4.