d in a return to MKS rules.  Instead,
the user preferences are respected in both cases.  Notice these can still
be overridden if desired.  To completely eliminate this simplification - i.e.
to have the user defaults reset to factory defaults - the
<code>dontusedimension</code> command can be used.  <code>uforget</code> can restore user
settings again, but only if <code>usedimension</code> frees it for use.  Alternately,
<code>kill(usersetunits)</code> will completely remove all knowledge of the user
default