Conventional methods
Straightedge/feeler gauge methods
The straightedge/feeler gauge methods which depend on the limited resolution of the human eye, produce a resolution of 1/10 mm (0.004"). This is far too inaccurate for most machines.
Dial gauges
Although dial gauges have a resolution of 1/100 mm (0.0004"), calculations tend to be complicated, and users must be highly experienced.
How accurate are dial indicator readings?
Sagging indicator brackets
This should always be measured before actual alignment reading are taken irrespective of how solid the bracket appears.
Low resolution
Up to 0.005 mm rounding error may occur with each reading -
for a total of up to 0.04 mm error in values used for result calculations.
Sticking/jumping dial hands
Sometimes the gauge must be tapped in order for the indicator needle to settle on its final value (which may still not be the correct one).
Play in mechanical linkages
Slight amounts may not be noticed, yet produce large errors in results.
Reading errors
Simple human errors that occur all too often when dials must be read under cramped, poorly-lit conditions and severe time constraints.
Tilted dial indicator
The gauge may not be mounted perpendicular to the measurement surface so that part of the displacement reading is lost.
Axial shaft play
This can affect face readings taken to measure angularity unless two axially mounted gauges are used
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