Digital, Dial & Vernier Calipers vs Micrometers
How to Choose Electronic, Mechanical, Fractional Inch, Metric Gauges
Nov 1, 2009
Mechanical dial calipers and electronic digital calipers can have similar high precision and accuracy. Depending on the model, both types can reach 0.01mm or 0.0005 inch resolution (precision), with 0.02mm or 0.001 inch accuracy. The difference between the two types is more a matter of robustness versus ease of use.
Prices are also about the same. They start as low as $20 and can reach over $100 for premium brands. Popular brands include Starrett, Mitutoyo, Neiko, Avenger, Fowler and Wixey. Most common are 6 inch models but 4 inch, 8 inch, 12 inch and other lengths are also available.
Digital calipers have the same mechanical requirements as dial calipers:
- Measuring edges should be straight and meet precisely without any visible gaps.
- The rail should be straight and the jaws should slide smoothly without being loose.
- A thumb roller fine adjustment allows precise closing of the jaws.
- A locking screw stops the jaws from moving.
Measuring edges and bars to support the following measurements are standard:
- Internal dimension (example: internal pipe diameter).
- External dimension (example: external pipe width).
- Depth (example: depth of hole).
- Step height.
Most are made out of stainless steel, though some are plastic. Plastic calipers can be accurate but the measuring edges are easily damaged.
Digital Electronic Calipers
Digital calipers have a numeric LCD display and are powered by a small button cell or coin battery. The LCD display is easier to read than the analog dial on mechanical calipers. Many LCD displays can easily switch between different measuring scales:
- Metric (millimeters).
- SAE, English or Imperial (decimal inches).
- Fractional inches (1/128 inches).
The main disadvantage is that they can be more fragile than mechanical dial calipers: less shock-resistant and more easily damaged by spilled liquid (waterproof digital calipers are available, but these are expensive and rare). The battery can also run flat at an inconvenient time. They are, however, less affected by dirt and metal shavings.
Some digital calipers can make simple calculations:
- Maximum measurement.
- Minimum measurement.
- Average measurement.
- Zeroing or tare at any position of the measuring jaws.
Useful battery-related features are:
- Low battery indicator.
- Auto off (after a few minutes of no activity).
- Auto on (when the jaws are moved).
A millimeter and inch ruler scale printed on the rail is not necessary, but can serve as a useful sanity check to ensure that the LCD reading is at least roughly correct.
Mechanical Analog Dial Calipers
High precision is provided by a sensitive analog dial. The dial's needle turns 360 degrees with every 0.1 inch movement of the jaws. This allows the dial to read to 0.001 inches. Some dials turn 360 degrees with every 1 inch movement of the jaws, giving a 0.01 inch resolution.
Some dials have a second scale for fractional (1/128 or 1/64) inches. Inch and millimeter scales aren't usually supported on the same calipers: two separate calipers need to be used. A rotating bezel allows the dial to be zeroed to the closest 0.1 inch.
The gears are affected by dirt. Even if the calipers can still work, accuracy may be affected.
Digital Micrometers
Digital micrometers provide 10 times more precision and accuracy: 0.00005 inches or 0.001mm resolution, with 0.0001 inches or 0.002mm accuracy. The main disadvantage is that they cannot measure lengths or widths more than 1 inch in size.
Vernier Calipers
Vernier calipers only have a few moving parts: the jaws, locking screw and thumb roller fine adjustment. This makes them virtually unbreakable and waterproof. Any dirt or liquid is easily washed off.
Resolution and accuracy can be almost as good as dial calipers and digital calipers. Unlike dial calipers, both English and metric scales can be built into the same calipers. Their main disadvantage is that the vernier scale is hard to read. This online simulation explains how to read a Vernier scale but in a real Vernier calipers, the markings are small and harder to match up.
Cheap (less than $10) brass and plastic Vernier calipers are available with 0.1mm or 1/32 inch resolution. These are easier to read and are good enough for carpentry and many other jobs.
The Best Calipers
The basic accuracy of digital and mechanical calipers is about the same. Digital calipers are easy to read and can easily convert between measurement systems. They are a good choice for engineers, mechanics and technicians who are careful with their tools and don't mind changing batteries every few months.
Simple Vernier calipers are tough and reliable, making them suitable for harsh environments. The performance of dial calipers is in between digital calipers and Vernier calipers. They are easier to read than Vernier calipers and are more resistant to liquid spills than digital calipers.
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