My current perl doesn't have a problem with

for (0..$#xdata) { push @frmt, [ $xdata[$_], \@{$ydata} ] }
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I know this is below where you think the script stops, but I notice that you don't do your data dump until 3 lines past the close...

I don't recall if perl ever had such a misbehaviour, but it could explain why things don't work the way you expect, since @xdata is populated in the part of the loop where you're looking at @_ instead of @values.

Please try

perl -e'for(0..$#a){print "$_\n"}'
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perl 5.6.1, active state build 633

I apologize for any misunderstandings... I took out the debugging statements when I posted (but one got through). The code most certainly doesn't get by the while loop. I had it printing the values of the time stamp and it stops at the corresponding value of the last time stamp in the file I tested it on. (by the way, the $_[0]variable I reference from time to time is just a quick hack I threw in ... it's an option to help in debugging somewhat, and somewhat as a test for a future feature. What it allows is for the user to specify that certain data has already been processed and is in a specified file (or the default one), so don't bother doing it again. I process certain files in this routine and get both data for an XY scatter plot, and also calculate the averages, so I threw that in.

And, $PART3 should not be set to 0 once I get it set. There are three button clicks in the file (represented by a 0 -- a 5 if none). I want the data from the last button click onward -- there are several little 'complications' with this reasoning, but it doesn't really affect anything here, and is a result of the data mainly.

I looked at it again this morning, and I'm still out of ideas...

I guess it's time for you to start removing statements from the loop until it works, to find the problem statement :(
--
Mike