A pitch log records the room, not the piano
A piano tuner's pitch log isn't really about the piano. It's a year of a room's humidity, recorded one cents deviation at a time, note by note.
A440 at the head, large. Twelve rows beneath it, C through B, a cents-deviation figure pencilled beside each note. Three are circled. A note in red: room too dry.
Nothing here measures the instrument. Everything here measures the weather.
What is a pitch log, and why does it really describe the room?
A row of twelve notes, each with a cents-deviation figure showing how far it's drifted from where it was last set.
A piano goes out of tune because its wooden soundboard swells and shrinks as humidity in the room changes, pulling every string with it. The tuner isn't really measuring the piano; they're measuring what a year of weather did to a large wooden instrument that happens to have strings and a keyboard attached. Log the temperature and humidity alongside the notes, as this one does — 23.6°C, 28% RH — and the whole page reads less like music and more like a weather station report.
Why does A read exactly 0.0 while every other note gets a number?
Because A440 is the reference the rest of the log is measured against, not a note that happened to come out perfect.
Every other figure on the page is a distance from that one point — D sharp two point six cents sharp, A sharp five point six cents flat — and none of those numbers would mean anything without a fixed zero to measure from. Setting A to 0.0 first is what makes the rest of the log legible as a single set of readings instead of twelve unrelated facts.
Which readings are worth circling on the log?
The outliers, not the whole row — the notes that moved enough to actually need attention.
A log where every note drifted by roughly the same amount says the room did something uniform: humidity changed, the whole soundboard responded together. A log where two or three notes are circled well outside that pattern says something more local happened — a string, not the room — and that's the distinction the circles exist to draw. Three circled against nine plain is more useful, and more honest, than circling nothing or circling all twelve.
Can a real tuner's pitch log go on a shirt?
The method is nobody's to license; the readings from a real piano, in a real room, belong to that piano's owner and the tuner who logged them.
Cents deviation, A440 as reference, temperature and humidity beside the notes — that's how the trade records a tuning, and a fact about how a trade works isn't property. A named concert hall's actual log, or a particular piano's service history, is a different matter, in the same way a real service card belongs to a specific watch rather than to the format. Invented figures on a real method get the whole thing right without asking anyone's permission.
Does this work for an instrument that isn't a piano?
Anything tuned by ear against a fixed reference, rather than built to a fixed pitch and left alone.
A choir's four numbers work from the same reference-note logic: everyone tunes against the same A, and everything else is a distance from it. A harpsichord, a pipe organ, a set of tuned percussion — anything that drifts and gets checked periodically has a version of this log, though few instruments make the room's humidity quite as legible as a piano's soundboard does.
Isn't a log about drift a strange thing to be proud of?
No — drift isn't a failure here, it's the whole reason the job exists.
An instrument that stayed put wouldn't need a tuner at all, and the log isn't evidence of a problem; it's evidence that somebody checked. The circled notes aren't a complaint about the piano. They're the parts of the room's story that were worth writing down in red instead of pencil.
Does a pencil log print well?
Yes, if the pencil stays pencil-grey rather than trying to look photographed.
The dense figures want more room than a real page gives them — twelve rows of small cents values will fill in at shirt scale unless they're set larger and spaced further apart than the tuner actually wrote them, because fine pencil detail is exactly the kind of mark that survives on paper and not on fabric. Charcoal on bone carries the log itself; the single red is worth keeping to the circled figures and the margin note, so it stays a flag rather than a second competing colour.
How do I get one made?
Describe the log at JustOG — which notes moved, the room conditions, and what the margin note says. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.
Designs other people have published are in the shop.
The piano was in tune in April. By August the room had an opinion about that.