Actually, the old default was the "Envelope Requirement" (Taylor Principle). ISO 8015 did something radical: It said that . That is, each specification on a drawing stands alone . A size tolerance does NOT control form unless explicitly stated. A flatness tolerance does NOT control parallelism unless explicitly stated.
In the world of precision engineering, silence is not golden. For most of the 20th century, a silent assumption ruled every workshop, every drawing board, and every inspection lab on the planet. That assumption was called the Principle of Independency —or more commonly, the "chain of defaults." If a drawing didn’t specify a tolerance, a machinist could assume one. If it didn’t mention a datum, the part’s natural edges would do. This unspoken language worked, but it was brittle, ambiguous, and often led to costly fights over who was "right." iso 8015
But the real victory came in global supply chains. After ISO 8015 was widely adopted (revised in 2011 as ISO 8015:2011, and eventually absorbed into the GPS master standard ISO 14638), a drawing from Japan could be read identically in Brazil, Germany, or South Africa. The standard eliminated the "translation errors" that had cost billions in scrap. Actually, the old default was the "Envelope Requirement"
ISO 8015 declared that the Principle of Independency was dead. In its place, it established the —wait, no, the names are tricky. Let's clarify: A size tolerance does NOT control form unless
Chaos. Shipping stopped. A $2 million order was held hostage by a missing "⌖" symbol on a drawing. The crisis forced companies to retrain entire workforces. The shift to ISO 8015 meant that every drawing had to be fully defined using GD&T (Geometric Dimensioning and Tolerancing) – flatness, straightness, circular runout, profile of a surface. The old "plus/minus" tolerancing was relegated to simple sizes.