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From: buxton@rmu.edu
Newsgroups: comp.graphics.apps.gnuplot
Subject: How to change the starting point?
Date: Thu, 6 Oct 2011 04:21:55 -0700 (PDT)
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Xref: x330-a1.tempe.blueboxinc.net comp.graphics.apps.gnuplot:629

Either you could change the xaxis or, if your data is x y then instead of 

plot 'data.dat' u 1:2

Try

plot 'data.dat' u ($1<63? 1/0: $1):2

Or

plot 'data.dat' u ($0<63? 1/0: $1):2

if your x-axis isn't your sequence number. I may have misunderstood though. What does your data look like?