In October a beta tester sent us a set of American drawings — and could not work with them. The reason went deeper than it first appeared: DrawingStamp Pro had no concept of a unit at all. Everything was silently millimetres. That has changed.
The principle: nothing is converted
The most important decision comes first, and it is deliberately unspectacular: values stay exactly as they are written on the drawing. .656 does not become 16.66. The unit is carried, stated and used to decide which general tolerance can apply at all — nothing is recalculated.
The reason is the inspector at the measuring device. Anyone holding a first article inspection report next to the drawing wants to see the same number. Every silent conversion is one more place for a rounding error to settle in where nobody will find it later.
The unit belongs to the drawing
The unit is not an application setting but a property of the sheet — two drawings open side by side can use different units. You set it under Settings ▸ Units, with a default for new documents.
Most of the time you will not have to. If the sheet says DIMENSIONS: INCHES, UNITS: INCH or DIMENSIONS ARE IN MILLIMETERS, DrawingStamp Pro recognises it, switches over and says so in the status bar. The anchor is the word DIMENSION(S) or UNIT(S) in front of it — a thread note such as INCH: INTERNAL THREADS 2B says nothing about how the sheet is dimensioned, and is not read as if it did.
Numbers without a leading zero
Inch drawings write values below 1 without the leading zero: .656, tolerances as ±.005. Detection now also picks up .039, Ø.827, R.039 and stacked limits such as Ø.283 +.004/-.000.
There is a second, less obvious point: dual dimensions in square brackets are not stamped. Ø5.512 +.080/-.080 [Ø140.00 +2.00/-2.00] produces one characteristic, not two — and it keeps its own tolerance.
General tolerance by decimal places
American drawings do not tolerance by nominal size range but by the number of decimal places. The title block then carries something like .X ±.1 .XX ±.01 .XXX ±.005.
DrawingStamp Pro reads that table off the sheet and gives it precedence over any configured standard — what is on the drawing governs. If there is none, the new standard Title block inch applies (.X through .XXXX, angles ±0°30′), editable in the standards editor.
Just as important is what does not apply for inch: ISO 2768, the plastics standards and the ISO 286 fits work in millimetres and give an inch dimension nothing. A dimension without a matching rule therefore stays untoleranced. That is on purpose — a millimetre value on an inch dimension would not be imprecise, it would be wrong, in a way that looks perfectly plausible in an inspection report.
The reports state the unit
What the drawing says, the output says too: the PPAP/FAI inspection report carries the header field “Einheit / Unit”, AS9102 Form 3 the field “Units”, customer templates the placeholder {{Unit}}, and the measurement plan names the unit in its title row.
What is not included yet
For completeness, so that nobody goes looking:
- No unit in the Calypso export. We know of no reliable key for it, and we do not guess here — we are waiting until we have a real inch measuring program in front of us.
- No ANSI fits (RC/LC/FN).
- No conversion between millimetres and inches. See above.
Availability
Imperial mode is included from build 1570 in the running beta. If you work with inch drawings and would like to test, put your name down via the beta form — inch drawings are exactly what we want to see more of right now.
Something missing, or does DrawingStamp Pro read one of your drawings wrongly? Report it through the support portal. This entire mode goes back to a report just like that.