Sorry I just found
https://www.physicsforums.com/showthread.php?t=306228
which is what I'm after.
fysics4fun made it clear:
"mpkannan makes it clear- you must look at everything in context before deciding the signs on everything. A question like "what is the sign on work" is too vague...
Homework Statement
I am wondering about the following conventions:
The work done by the gas is positive if the gas expands,
and negative if it is compressed.
Conversely, the work done on the gas by external force
(e.g., a moving piston) is positive for compression, and negative when...