My function "autoscales", so it would output "4.56u". But, I could see the value in having a mode where it could fix the scale to always output "u", or whatever the user specifies. Here is a sample of what my function does (left column is input, right is output):

                     1234 --> 1.23k
                    50000 --> 50k
                     5000 --> 5k
                      500 --> 500
                    0.012 --> 12m
               0.00055555 --> 555u
                     5e-5 --> 50u
                     5E-5 --> 50u
                  5.0e-05 --> 50u
                   -193.7 --> -193
                       -5 --> -5
                  -0.7895 --> -789m
       555555555555555555 --> 5.56e+17
     0.000000000000000777 --> 7.77e-16
                  9876543 --> 9.87M
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Obviously, this is only used for very coarse estimates. It does not handle rounding or precision correctly.