The SI prefix ladder in format_measure() was gated on a non-empty unit, so two
decimals of a small unitless value printed `0.00` -- the reading gone, not merely
coarse. That is a whole class of channels rather than a corner: a CONFIG need not
declare a unit, and a math channel never has one. Below 1e-12 the same loss
happened even with a unit, so that range falls back to three significant digits.
With no unit the prefix goes tight against the number (`585.24m`), since the space
exists to separate the number from its unit and a spaced `m` alone reads as metres.
The mock declared `unit="V"` for every data signal, which is why no probe could see
this; it now takes `--unit ''`.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
