mechanical · 28 minutes · Official OETT Aligned
Reading Measuring Tools
Read the marks, then work out the measurement
What to know
- units: inches, feet, or millimeters
- value of each gap between marks
- pointer or reading line
- caliper: a tool for measuring widths and gaps
The labels and marks tell you the measurement. The size of the picture on your screen does not.
The core rule
Find the unit, work out the value of each gap between marks, then count from the correct starting point.
First read the numbered marks. Divide the difference between two numbers by the number of equal gaps between them. Then count to the pointer or edge of the object. If the object does not start at zero, subtract its starting reading from its ending reading.
Worked examples
Example 1: easy
Between 0.020 and 0.030, five equal intervals represent 0.002 each.
- Subtract the labeled values: 0.030 − 0.020 = 0.010 inch.
- There are five equal gaps, so each is 0.010 ÷ 5 = 0.002 inch.
Divide the numbered distance by the number of gaps to find each gap value.
Example 2: medium
A pointer at the third 1/16-inch tick reads 3/16 inch.
- Each small gap is 1/16 inch.
- Count three gaps from zero: 3 × 1/16 = 3/16 inch.
Follow the scale from zero and count gaps to avoid counting one extra mark.
Example 3: hard
Combine a main-scale reading with the aligned vernier mark without counting the zero twice.
- On a vernier caliper, read the main scale just before the zero on the smaller sliding scale.
- Find the sliding-scale mark that lines up with a main-scale mark. Add its value to the main reading.
The main scale gives the larger amount; the sliding vernier scale gives the small extra amount.
Common mistakes
The longest mark always means one whole unit.
Longer marks help you read the scale, but the numbers tell you what each gap is worth.
Put it into practice
Use guided explanations, check your answers, and try a new variation.