Thank you both for your replies.
Ingo, I think your suggestion that an 'unclean' shutdown could be the cause is probably correct as my laptop battery was more or less completely flat by the time I called it a day. Mind you, at that stage, your very sensible idea to shut down and restart to check the polar diagram would have been too late to continue the session if all was not well. Next time I go up there, I'll do a couple of shutdown/restarts earlier and copy/paste the D012.dat files to another folder at that stage. I reckon, by the number of 'hits' I was getting, the PD would be more or less the same after about one hour as two.
Rod, if after a shutdown/restart the diagram was up to date but it reverted to the previous one on final shutdown, would there not be only data for the previous one in D012.dat?
Unfortunately, I’m not the brightest shilling in the till with Excel and I would be pleased if you could explain how to create a chart from the data
If you would be good enough to do so, perhaps a PM would be best as probably almost all other members will know.
Thanks again,
Regards,
Syd