Hello DuncanG,
I have tested this, and it looks like this is because of a bug, so I added it to our to-do-list. We want to fix this in an update for ARCHICAD 22, you will find it in the Release note as fix #261234.
The function should return the value as a string in the format you set for that value type in calculation Units and Rules. Unfortunately the issue is that it is not taking Calculation Units and Rules into consideration, it uses a kind of random precision when used with Imperial units (with fractions). Metric units and decimal feet/inches work fine.
Unfortunately the only workaround I could find is using decimal feet/inches instead of fractional feet & inches. I think even though it looks weird, it might be enough to get by with until the fix, but if you find a better solution, please let me know!
Regards,
Daniel Alexander Kovacs
Professional Services Consultant
GRAPHISOFT
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