Units

Choosing what an item reports in, and supplying the dimension a derived unit needs.

An item reports in one unit, picked from its geometry's catalog.

Changing an item's unit

Pick the new unit on the item. If it is a direct unit the change is immediate. If it is a derived one - a unit that cannot be worked out from the drawing alone - a calculator opens asking for what it needs:

A depth or thickness can be typed in inches or feet. The unit you typed in is remembered for display; the stored value stays canonical, so switching the display never changes the quantity.
A density, rate or weight is typed in the unit shown beside it.

What you enter is kept on the item and shown back as a formula you can edit later, rather than disappearing into a multiplier.

Area units

Unit	Kind	Needs
SF, SY, AC, SQ, m²	Direct	-
CF, CY	Derived	Depth (default 4 in)
TN, LB	Derived	Thickness (default 2 in) and Density (default 145 lbs/cf)
GAL	Derived	Rate in gal/SY (default 0.05)
LS	Direct	-

Length units

Unit	Kind	Needs
FT, YD, m	Direct	-
SF, SY, m²	Derived	Width (default 1 ft)
LB, TN	Derived	Weight in lbs/ft (default 1)
CF, CY	Derived	Width (default 1 ft) and Depth (default 12 in)

Count units

Unit	Kind	Needs
UN, EA	Direct	-
LF	Derived	Length each (default 1 ft)
SF	Derived	Size each, in sf (default 1)
CF, CY	Derived	Volume each, in cf (default 1)
LB, TN	Derived	Weight each, in lb (default 1)

Notes

The catalog is fixed. A project cannot add to it, and a unit name one project introduces does not leak into the next project opened in the same session.
ft-in is hidden from the picker but still loads, so old projects that used it keep working.