 to change an existing value in the current lens prescription,
use the <strong>CHG</strong> command. If, for example, the radius of
curvature of surface number 2 had been input as 4.094 instead of 40.94
and the thickness of surface 3 had been left equal to the default
(0.0) instead of input as 11.05, the following commands would be used
to make the corrections:</p>

<p><strong>
    U L<br>
    CHG 2<br>
    RD 4Ø.94<br>
    CHG 3<br>
    TH 11.Ø5<br>
    EOS<br>
</strong></p>

<p>If you had failed to type