Machinist level specs seconds vs tenths/10"

AGCB97

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I'm looking at level specs of various levels.
Starrett gives 0.42 mm/m or 80 to 90 seconds
How does this compare to .0005/10"
My math seems to not work

Thanks
Aaron
 
10 seconds of arc equals approximately .0005"/10" or .0006"/12". A second of arc is 1/3600 degrees. The sine of 1 second of arc is 4.848 x 10^-6 (.000004848) That times 10" is .00004848". For very small angles, the sine, tangent, and arc in radians (2π radians equals 360º) are close to equal so 10 seconds of arc = .00048"/10".
 
Per Starrett, Main level vials have graduations that are approximately 80-90 seconds or .005" per foot (0.42mm per meter)
 
Per Starrett, Main level vials have graduations that are approximately 80-90 seconds or .005" per foot (0.42mm per meter)

Should that be .0005" per foot?
 
Starrett' 98 Series levels are .005"/ft. Their 199 series level is .0005"/ft.
The bottom line is that the 98 series is not good enough to precision level a machine tool such as a lathe, but is adequate to level such as milling machines, drilling machines, etc.
 
The bottom line is that the 98 series is not good enough to precision level a machine tool such as a lathe, but is adequate to level such as milling machines, drilling machines, etc.
Thats good enough for checking for twist i a lathe bed as well as levelimg, let it sit in use and see if it holds tolerances or check with a 199 Starrett or a King gage.
 
I quite disagree with the above statement, a Starrett #98 is nowhere near sensitive for lathe alignment, it is only good enough for rough leveling in preperation with a .0005 resolution (or better) level for final alignment.
 
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