Issues with HP DesignJet Series PS Printer

Question
We have issues when trying to print to HP Large format printers, T920PS T1500PS and T2500PS.
Grid does not appear to be uniform.
Dots are not round.

Answer
There may be several reasons to these problems.
Make sure that you are using a PS print driver (if different exists).
If you are printing from a PDF and using Adobe Tools (Reader etc.), you need to turn off scaling and/or centering (in the print GUI); should be sent unmodified.
If printing from a postscript file (.ps) using GSview, select "Postscript driver" as "Print Method" in print GUI.