Old GD&T Symbol "~"

[brimartinez]

I'm hoping I can find some help here on the Cove.

We are having a hard time trying to find the interpretation of a symbol found on an old Northrop drawing. I have attached a part of the drawing.

The PO we got from our customer states to interpret dimensions and tolerances per ASME Y14.5 in lieu of 20Y201.

Only problem is that ASME Y14.5 doesn't have this symbol "~".

Thank you!

 

[Miner]

Wow, is that old!

It is a flatness call out used in MIL-STD-8A (1953).

See page 10 of this US Army memorandum report.
.

 

[brimartinez]

Thank you so much!!

We figured it had to do with flatness but were going in circles trying to determine "how" we knew it.