A calculator result stays in the sum as `a`, handed to evaluate with
its whole value, so 1 ÷ 3 = × 3 = gives 1; sign turns it and delete
takes it. Equals waits on a dangling operator. The converter's reading
wraps in its box rather than ending in an ellipsis, and tests hold
Control, the = key, a point after a result and the six digits.
misc::Calculator works a typed sum in forms::evaluate's precedence,
from a pad or the keyboard; Enter is equals while the calculator
itself has focus, and Escape clears or passes on. misc::UnitConverter
reads an amount in another unit across seven kinds, with a swap.
Both show numbers through format::significant, which rounds through
Rust's exponent form.
ZacharyZhang-NY