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In CGS I found both ESU (Charge) and Angstrom(length), but I did not find unit for the electric dipole moment.
I can't answer the question WHY Debye are not built into Mathcad, but its easy enough to define your own unit anyway

Depending on the way you define it, results may differ in the last (15th, 16th) decimals
One might say much about the measurement unit that mathcad provides. Those absent, we have to define them in a separate file that we could include as reference in the worksheets we are interested in. In the case of the dipole moment, however, you can define the unit of measure as follows:

