R 1h 2 2(R 1 + R 2 )2
=
Similarly, b =
R 2h 2 2(R 1 + R 2 )2
Therefore, (a+b) = =
very nearly
(R 1 + R 2 )h 2 2(R 1 + R 2 )2 h2 2(R 1 + R 2 )
3) Error due to contact pressure: The variations in the contact pressure between the anvils of the instrument and the work piece being measured produce considerable difference in reading. The deformation of the work piece and the anvils of instrument depend upon the contact pressure and the shape of the contact surfaces.
Stylus
Workpiece deformation
Stylus deformation Work piece
4) Error due to vibrations: The errors due to vibrations can be avoided by a) locating the laboratory away from the sources of vibration b) keeping slipping cork, felt, rubber pads under the gauge c) mounting the gauge pedestal or floor sections on tar mastic