"2007-User" wrote...
Have you seen any add-on utility that can add such capability to
excel? it would be so nice. In MathCAD you can change the units
like "lb" to "kg" and the result will change automatically...
....

AFAIK there are no such add-ins, and if there were they'd either only
work as functions operating on specially formatted strings, e.g.,

=UNITMULT("5.3_g","12_m") - "63.6_g.m" [momentum]

similar to how Excel's ATP IM* functions operate on complex numbers,
or using Calculate event handlers to alter number formats, e.g.,

A1 containing 5.3 formatted as "0.0\_\g" and B1 containing 12
formatted as "0\_\m", with C1 containing =A1*B1, so evaluating to 63.6
and with the Calculate event handler finding the number formats of A1
and B1 and changing C1's number format to "0.0\_\g\.\m".

While I can appreciate why you might want this, Excel is a GENERAL
tool for relatively SIMPLE calculations. IOW, it's a BUSINESS
calculation tool. Some people may try to misuse it as mathematical
software (like MathCAD, MatLAB, etc.), but Excel simply lacks much of
the functionality of mathematical software. It may be possible to add
functionality to Excel, but the result won't be any cleaner than the
ATP's IM* functions (and for arbitrary units, it'd be MUCH dirtier),
and it'd noticeably affect Excel's recalc speed.

Still, there's always Google search. Google shows only 22 hits when
searching for +Excel +"MKS units" +"add-in", and most of them are for
the same add-in, ChangeUnits.