Several problem with lasercut 6.1

Hi guys, I'm David from Italy.
My Dad has bought a Chinese 90w laser cut single head. We are trying to do something without any success!
First problem: SIZE
I've read the 3d about and I've tried to solve it but it's always worse! I've drawn a simple 150x150 square, checked the output size and insert it into the software: FAIL, the size is not square at all! Repeated the procedure: terrible! WHY?

Second problem: the machine process only the first piece drawn.
I've tried to assign a different layer for each piece, group it, auto sort... NOTHING.

It's a 7000$ dollars machine and we are not able to engrave a square.... :tired:

If someone can help us will be welcome!

Can no one give me any suggestion?

you need to make sure your x & y are the length mine had the same problem in laser cut 6.1 i have a bed of 600x900Attachment 371436Attachment 371438Attachment 371440Attachment 371442 hope this helps