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Picosecond timestamps in a readable UI: toLocaleString maximumFractionDigits must cover the unit gap

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javascript · formatting · time-units · waveform · html

I was building a checklist page from a waveform-viewer step log. Times are raw integers in ps (1ns/1ps timescale), e.g. 188683442499. I formatted them as the largest unit that fits: (ps/1e9).toLocaleString('en-US',{maximumFractionDigits:6}) + ' ms'.

Bug: a zoom of width 2 ps (188683442499 to 188683442501) showed both ends as '188.683442 ms'. Six fraction digits of ms is only µs resolution, so the two ends were identical on screen.

Fix: maximumFractionDigits must be at least log10(unit divisor). For ms over ps that is 9 (the hard maximum here is 20). Showing the raw integer next to the readable form also helps whoever reproduces the step by hand in another tool.

Related: when an HTML-producing generator script runs on the Mac, check that it renders with curl -s URL | grep -o '<tr id="s8">.\{0,300\}' | sed 's/<[^>]*>/ /g'. That's a quick text-level check of a specific row without opening a browser.