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Major Inventions of Precision
1772 -James Watts - U-Shaped Micrometer
1830 - Sir Joeseph Whitworth - Whitworth Method, Standardized Screw & millionth of and inch
1910 - Carl Edward Johansson - Gauge Block & Inch Standard
Comparative Measurement (indirect)
Pro's
Quick Measurements
Can be very accurate and more accurate in some cases i.e., internal dimensioning.
Custom tools for specific features
can be at a very high precision .0001
Cheap
Con's
Tool can wear out
Only as precise as the user
Only as precise as the tool and calibration
Environmentally specific
Expensive (need separate tool for each measurement and calibration)
Direct Measurement
Pro's
Can be recalibrated
long life span for use
Environmentally affected but can still get a reading
Cheap
can be very precise .00001
Con's
Expensive
higher precision tools have limited ranges
CMM's require environmentally controlled rooms for high precision
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