Theme

Typing measurements

You can type instead of dragging, nearly everywhere.

A little arithmetic

Anywhere a length is typed, it can be worked out as it is typed. The answer shows at the end of the typing box as you go - = 8'-8" - and Enter uses it. Space is a space while you type, so a sum can be written with them; Enter is what uses it.

The typing box, at the right of the command bar, colors what you type so it can be read at a glance: the figures in amber, the foot and inch marks in green, the operators of a sum - + -- * / and brackets - in pink, and the x between two sizes in violet. The bar's second line is what the program just said, with names, lengths, commands and keys picked out the same way; right-click the bar to copy it.

TypedIsWhy
8' + 8"8'-8"plus
8'24" + 3'4"13'-4"8'24" is ten foot - it always was
10' - 3'4"6'-8"a minus with a space either side
6-8-0--2-4-04'-4"two dashes are always a minus - truss on both sides, all from the number pad
6-8-0+2-4-09'truss adds too
8'6"-3"8'-3"a dash straight after an inch mark is a minus - a length never goes on past its inches
10'-3'4"6'-8"a dash after feet, with feet of its own on the other side, is a minus
8'17" / 24'-8 1/2"a slash is divide - unless it sits between two digits
(8' + 4") * 216'-8"times, and brackets first
3 * 2'6"7'-6"a plain number times a length
8' + 210'a plain number in a sum is feet, as a bare number always is

What stays a length and is never a sum:

So a dash is a minus when it is two dashes (--), when it has a space either side, when it comes straight after an inch mark, or when the other side has feet of its own. Two dashes is the one to remember: truss notation never has two in a row, so -- is a minus whatever is either side of it, and the whole sum goes in from the number pad. A length times a length is an area, not a length, and is refused; so is dividing by nothing.

What it looks like

A rectangle being given its size by typing.
One corner clicked, then 8x5 typed instead of dragging the other. The hint line says what forms it will take; Enter lands it.