I have a A150 Snapmaker. To calibrate you use an auto program, that makes a kind of messurement on 9 points. After that you must tune calibration by hand and save.
I have done this calibration many, many times. I use a first level test, to see the result
Every time I have a problem. The middle of the bed is ok, the corners er NOT. My conclusion is – the bed is not 100% even
I can’t find a way to upload picture - sorry
Do you have the same problem?
The bed is not perfectly flat, and does not heat evenly either. Furthermore, the older firmware versions have a bug where the points that are probed during levelling aren’t quite where the machine thinks they are.
Upgrade your firmware to version 1.12.2 if you haven’t already (not 1.13.x, as this series introduces annoying wifi bugs). Check to make sure you assembled your machine with everything the right way up (seriously—there’s an ambiguity in the quickstart guide that has caused many people to make a mistake assembling the bed).
If the results you get are still not acceptable, consider modifying the machine with a glass bed. Personally, I’m willing to settle for “good enough” (that is, prints stick firmly, even if some have an imperfect bottom surface).
Thank you Ellory
I’m Danish and my English is not so good 
All firmware is updated. I will messure temperature in the sides of the bed, and see if thats the problem
I’ll add that levelling the bed while the heat is on is a frequently requested feature, and I think Snapmaker has said they’re working on it. In the meanwhile, the best you can do is use gcode commands to heat the bed up, then turn the heat off and level the bed as it’s cooling. Some people have gotten okay results from this.
Good luck.
Post some pictures of your machine assembly, there should be a upload button after a bit reading (maybe posting? - not sure) in the forum.
The latest firmware should handle those uneven beds with no problems.
Thank you for all good feedbacks. I have made a callibration with a hot bed - now it’s nearly ok. I messured temperature - there is a difference of 4 degrees from center to corners.