Using units in Prime is extremely cumbersome compared to MathCad 15. Although I've tried to define new units globally, using the units labeling it doesn't seem to work. In combo boxes, can't define units containing exponents. There are common units used in Chemical Engineering that should be available such as mbar, cP, etc.
The combo boxes seems to be very badly and sloppily integrated in Prime (especially concerning units). The same was the case with the charting tool which never was improved and still does not support units at all.