Oh both are great ideas. Thanks guys. I will definitely use them. What I was referring to specifically is the z deviation. Sorry for my bad introduction. My idea was to take a long enough spirit level and put a small laser on it. The spirit level would be placed at one end of the table in parallel to my y axis. Now I would draw a line on the wall which lays behind the other end of the table. The further away the better. To find the exact same height I would use a long hose filled with water. Then I would make a mark every inch on that line.
Finally I would adjust the laser so that it's placed on one end of the level and pointing to the first mark on the wall. When that's setup I would attach a light sensor to my end mill. Beginning at one end of the x axis I would lower it until I get a signal from my light sensor. Now moving on I take several data points running down the x axis. When it finishes I would place the laser an Inch further on the spirit level and let it point to the second mark on the line on the wall. I hope that explains it better. What are you guys thinking about it?

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