s">rpn Mathematics</a>).
<p>
Variables are often useful in `<font color="#82140F"><code>if</code></font>' statements.  Here are some
examples:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
read .num_pts.
if .num_pts.
  show "There are some data"
  read columns .num_pts. x y
else
  show "There are no data"
end if
# ...
read .latitude.
if {rpn .latitude. 10 &lt;}
  read .num.
  read .num. x y
  draw curve
else
  show "Skipping data North of 10de