A Vernier caliper is a measuring instrument for internal or external dimensions of an object, as well as for distances between different points; this tool is capable of providing more precise measurements than is possible with other more known methods (eg the ruler) and has a maximum error of only 0.05 mm. Manual gauges can have one scale in decimal metric units and one in imperial units, but sometimes only one of the two.
Steps
Part 1 of 2: Prepare the Tool and Tools
Step 1. Start recognizing the various parts of the Vernier caliber
This instrument has two pairs of appendages, called beaks or rods, of which the largest is used to measure external diameters while the other is used for the internal dimensions of objects; some models also provide a depth measurement. The main scale is fixed, while the Vernier scale (or vernier) is the part that flows, opening and closing the beaks.
Step 2. Learn to read gauge scales
Each of these should be read like that of a classic ruler: generally there is a main one that indicates centimeters (or inches), with smaller subdivisions between the various units; the sliding scale, on the other hand, should have an inscription indicating what it represents.
- If there is no caption you can assume that each notch measures 1/10 of the minor division on the main scale: for example, if the minor major subdivision represents 1mm, each notch on the sliding scale will be 0.1mm.
- The main scale is life size, while the one on the slide is "enlarged", providing a simpler reading; it is precisely this system that guarantees the Vernier caliber its greater precision than similar instruments.
Step 3. Check the scale of the minor subdivisions
Before you start measuring, count the number of marks between two units on the fixed scale, then work out the distance indicated by each mark.
To obtain this information you will have to divide the distance between two main notches by the number of secondary notches between each of them; let's say, for example, that each large line represents one centimeter and that between two of them there are 5 small notches: you will have to calculate 1 cm / 5 = 2 mm, which is the distance between two minor lines.
Step 4. Clean the object to be measured
Dust it carefully with a cloth, in order to remove grease and dust particles that could decrease the accuracy of the measurement.
Step 5. Loosen the screw
If your gauge has a set screw, unscrew it slightly before starting.
Turning a screw clockwise will screw it in, while to unscrew it you'll need to turn it counterclockwise
Step 6. Shut the beaks
Before measuring the object, close your jaws and check that the scales indicate a null measurement, checking that the instrument is not misaligned; otherwise you will have to check what is the systematic error of misalignment of the scales ("zero error" or "offset") and correct all the measurements you will perform.
- For example, if the zero on the cursor scale were to line up with the 1mm mark on the fixed scale, you would have a zero (or offset) error of +1 mm; in practice, you will have to subtract 1mm from all measurements.
- If the zero of the cursor aligns to the left of the zero of the main scale instead, you will have a negative error. Move the cursor until the zeros line up, while checking how much another notch moves; for example, if the notch indicating 0, 5 mm were to move from 1 to 2, 1 mm, the offset will be 1 - 2, 1 = - 1, 1 mm. You will therefore have to add 1.1 mm to each measurement to correct the error.
Part 2 of 2: Using the Caliper
Step 1. Place a beak on the object
The instrument has two types of beaks: the larger ones tighten around the object and measure external distances; the others, on the other hand, must be inserted into an opening and widened until they touch the edges, to take internal measurements. The two pairs of beaks move together when you slide the cursor; once the gauge rods have been positioned correctly, tighten the fixing screw (if present).
Step 2. Read the measurement on the main scale, at the point where the zero of the cursor is
The fixed scale generally measures the units and the first decimal value, exactly as if it were a ruler, so you just need to check the zero position of the sliding scale.
- For example, if the 0 of the cursor were in correspondence with the 2 cm mark, this would be the measurement; if you were to line up 6 notches of 0, 1 cm after the main 2 cm notch, you will have 2, 6 cm.
- If the alignment point was between two secondary marks, use the lower value; do not try to estimate a more precise measure than that provided by the fixed scale.
Step 3. Read the slider
Find the first notch that perfectly matches any line on the main scale; this will be the value of the second decimal number.
- For example, let's say that the 8 of the cursor is aligned with a main notch: if the sliding scale represented increments of 0.1 mm you would get 0.8 mm.
- It is of no importance which notch on the fixed scale the cursor aligns with; we are focusing on the latter, so leave out the first (whose measurement we have already read).
Step 4. Add the numbers
Add the value of the main scale and the one read in the Vernier scale to obtain the final measurement; make sure you use the appropriate units for both, otherwise you will get wrong values.
- In our example we measured 2.6 cm in the fixed scale and 0.8 mm in the mobile one: our measurement is 2.68 cm.
- The numbers are not always so simple to add: for example, if the centimeter scale indicated 8, 5 and the vernier indicated 12 tenths of a millimeter, the sum would be 8, 5 + 1, 2 = 9, 7 cm.
