HP 39g Master Manual page 196

To use a different shape you need only change the points in matrix M2. If
your new shape has more than three vertices you will need to change the
TRange values in the PLOT SETUP view. It is not a good idea to use shapes
that are symmetrical, like squares, as it makes it harder to recognize
transformations.
Calculator Tip
Warning: Due to a bug which existed in the hp 38g and
hp 39g, this aplet cannot be sent from one hp 39g to
another using the infra-red link. The formulas in the SYMB
view often become corrupted during the transfer and need
to be re-entered.
This is not a problem for two reasons. Firstly, the transfer
would require sending not only the aplet but the matrices
too: by the time this is done it would probably have been
faster to have the class set it up themselves. Secondly, if
the class is not to regard this as 'magic' then they need to
understand how the aplet works. This is best
accomplished by having them set it up themselves. You
might even consider allowing them to first play with
drawing shapes of their own invention using a single matrix
and only X1 and Y1. This will show clearly why the
TRange settings are important, and how the values are
extracted from the matrix.
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