SAE AS8879 is derived from original standard MIL-S-8879. Here is the section on Lead and flank angle (3.4.5.2 from Rev C):

The lead shall be the number of thread starts divided by the number of threads per inch. The flank angle shall be 30 degrees. The diameter equivalent of variations in lead (including helix variations), or flank angle, shall not exceed 0.4 of the total pitch diameter tolerance for each element individually.

i still do not get. say pitch diameter tolerance .005". 40% is .002". how to equivalent to degree/minute/second?
thanks.

Check out section 3.4 Errors in flank angles in relation to pitch diameter of this document:

NPL NOTES ON SCREW GAUGES
http://www.npl.co.uk/upload/pdf/screw_gauge_bookle...


Here are some other links that discuss this topic:

https://www.google.com/#q=%22diameter+equivalent%2...

TVP, thank you.
sorry for my stupidity.
1-12-UNJF-3B. pitch diameter .9459/.9516, 40% of this tolerance is .0023".
1-12 has pitch (p) .08333.
from 3.4 of the booklet, .0023 = .0091 * .08333 * (FLANK ANGLE DELTA)
IT RESULTS delta flank angle 3.05 degrees !
i do not know where i did wrong.
even, it results a meaningful small number, how it is measured in industry?
thanks again.