Bill Gates's 1976 "Open Letter to Hobbyists" claimed fewer than 10% of Altair owners had paid for the BASIC he, Allen, and Davidoff wrote

On February 3, 1976, Bill Gates published his "Open Letter to Hobbyists," reproduced in the Homebrew Computer Club Newsletter (Vol 2, No 1). It is widely treated as the founding document of the framing that unpaid copying of software is theft. Its central grievance was quantitative: Gates wrote that "less than 10% of all Altair owners" had actually bought BASIC, despite widespread use of the interpreter — a rate he presented as making continued development uneconomic.

The BASIC in question was the work of three people — Paul Allen, Gates, and Monte Davidoff — a fact the program's own source comments recorded even though one of the three, Davidoff, was later left off the copyright notice (claim-davidoff-wrote-third-of-altair-basic-uncredited). The same product that grounded the anti-piracy argument was thus also the site of an internal credit erasure, and the erased author would decades later oppose DRM copy-control technology (claim-davidoff-2001-opposed-cprm-drm).

The <10% figure is a specific quantitative claim, so it needs a Tier 1–2 home. It is quoted here from DigiBarn's transcription of the letter (Tier 2) — a faithful-looking reproduction of a primary document, but a transcription, not the original printing. Because the number is the load-bearing element, an independently verified primary printing would harden it.

This evidentiary shape is shared with claim-amari-1968-saito-experiment-primary-read: each note rests on a single imperfect intermediary — a web transcription here, a partial OCR scan there — what medieval Roman-canon law would call a half-proof (semiplena probatio), insufficient without a second witness (claim-roman-canon-law-rated-one-witness-equal-to-a-private-document). The "independently verified primary printing" this note asks for is precisely that second witness.