** Using WeBWorK **

OK, I can make a pull request with all this in time for the 2.13 release. If you want something sooner, I can talk with you about making local modifications to your WeBWorK server. (But if you are using someone else's sever, or the MAA hosting service, it won't be an option.)

Is the "m" in "mpsi" ever interpreted as "milli"?

At https://github.com/openwebwork/pg/blob/master/lib/Units.pm, you can see how units are defined. "lb" is:

'lb' => {
'factor' => 4.4482216152605,
'm' => 1,
'kg' => 1,
's' => -2
},

So it's 4.4482216152605 m kg / s^2. In fact, if the answer is "1 lb" (aka "1 lbf"), you can enter "4.448 m kg /s^2" and it will be marked correct.