You need to arrow right after typing units to get out of the units.
5 crtl+shift+u ft (right arrow) + etc.....
This is where I believe your issue is.
**edit added** I had a quick look in the user manual, and that minor detail to arrow out of the units was not mentioned, but it's similar to getting out of an exponent or denominator so just a minor miss as it was probably implied.
So initially I thought it would automatically assign to the first units mentioned in the equation, but that doesn't matter. It seems to be preset to standard SI units.
It would be nice to have a list of preset preferences the worksheet would work as. (ie units settings and digits - it would be nice to have a preset number of decimal places shown. 3 decimal places I think was chosen as a happy medium. However for example - the smallest medium of measure for carpentry is 1/16" which is 0.0625 ( I mean mostly - there are some tape measures out there with 1/32" scales - good for machining, milling or lathe work I guess ultimately at that point you're working with micrometers and calipers which are likely digital). If it was going to be a set value personally I would have gone with 4 decimal places but ultimately I would let the user choose in a user preferences.