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Logic behind ASME 14.5 1.6.2(a). No Zero before decimal point.

Logic behind ASME 14.5 1.6.2(a). No Zero before decimal point.

Can someone explain the logic behind ASME 14.5 1.6.2(a) which states:
1.6.2(a) A zero is not used before the decimal point for values of less than 1 in.

To the contrary 1.6.1(a) for metric units (millimeters) states the opposite:
1.6.1(a) Where the dimension is less than one millimeter, a zero precedes the decimal point.

Seems to me the leading zero before the decimal point should be required always, regardless of the units.
Otherwise, 0.25 inches could look like 25 inches on a poor quality reproduction of the drawing. That decimal point is tiny and can end up not being printed clearly or at all.

Conversely, a random spec or printing artifact could look like a decimal point. If it was unfortunately close to a 25-inch dimension or worse drawing note it would look like 1/4 inch instead.
That is; "Is that a spec or a decimal point" is totally remedied by a leading zero before the decimal point.
In a drawing note, it would not be as apparently wrong as it would be in a dimension. In a dimension, the scale of other part is a clue. So is the relative size of other dimensions. Not the case in a drawing note.

So why a zero before a mm dimension and not before the inch dimension?

If it's just to distinguish between mm and inch dimensions that seems like a poor way to do it.
Generally, all dimensions are in either SI or Imperial units and stated so in the title block or notes. That's the best place to check.
Dual dimensions on a drawing only emphasize the difference. Lack of or presence of a zero before the decimal isn't so necessary. The drawing will have a note somewhere explaining which is which, top or bottom dimension, side by side with alternate units in brackets or parenthesis.

What am I missing?

RE: Logic behind ASME 14.5 1.6.2(a). No Zero before decimal point.

I say the standard is wrong. USE the zero in both cases. Only batting averages are OK without the leading zero.

"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Logic behind ASME 14.5 1.6.2(a). No Zero before decimal point.


Any suggestions on the trailing zeros? ANSI/ASME keeps them, but ISO/SI/DIN/JSI drops trailing zeros.

And what do you think about decimal points: period or comma?

RE: Logic behind ASME 14.5 1.6.2(a). No Zero before decimal point.


What you are missing is the time frame in which this standard was first developed.

Back in the days when manual drafting was done, the less you lettered the faster a drawing was finished.

John H. Dunten, CD
Certified Drafter

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