Unit conversion in Petroleum Office is based on UnitConverter() Excel function which is part on add-in function library.
It has the following parameters:
There are 3 types of units you can use with UnitConverter().
1) Registered Units
Add-in has built in extensive library of units (~1500).
By clicking the "All Units" button on Ribbon, you can find the full list of registered units, search through and copy abbreviation for selected.
2) Scaled Units
It's a combination of value with registered unit separated by space, "640 acre" for example.
3) Unit Expression*
You can create your own unit using simple syntax by combining any registered units and the following characters: * - as multiplication, ^ - as power. Here is an example: