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use strict;
use warnings;
...
  return [ $centerX + $radiusX*cos($radians)
           , $centerY - $radiusY*sin($radians) ];
}

sub drawArrow {
  my ($xEnd, $yEnd, $start, $extent, $arrowLength) = @_;
...
   $can->createLine($xEnd, $yEnd, $xEnd+$xArrow, $yEnd-$yArrow);
   $can->createLine($xEnd, $yEnd, $xEnd+$yArrow, $yEnd+$xArrow);
}