About us

Why we built it

A vernier caliper is not hard to understand. It is hard to learn, because the skill is entirely in your hands and eyes: sliding the jaws to a firm but gentle stop, finding the main scale division just before the vernier zero, and then scanning twenty or fifty tick marks for the one pair that lines up. No amount of reading about the formula substitutes for doing it.

The problem is access. A physics class of forty shares four calipers. A student revising the night before an exam has none. Someone taking a first machining job has one on the bench but nobody free to check their readings. In all three cases the instrument is the bottleneck, not the idea.

So we made an instrument you cannot run out of. Drag the jaws, read the scale, check your answer, repeat. That is the whole product.

What the simulator does

• A caliper you can actually drag

  The jaws move under the pointer or your finger, the scales move with them, and the reading follows the geometry rather than a number chosen in advance.

• Three least counts, metric and imperial

  Switch between 0.1 mm, 0.05 mm and 0.02 mm verniers — the ones on real school and workshop instruments — or change to inches and read in thousandths.

• Zero error you can dial in

  Introduce a positive or negative zero error and watch it quietly offset every reading, which is exactly how it behaves on a dropped or worn instrument.

• A practice mode that marks you

  The tool sets a reading, you say what it is, and it tells you whether you were right — and, when you were not, which of the six standard mistakes you made.

How it is built

The site is a static site. There is no account to create, no login, no database and no server-side processing of anything you do. The caliper is drawn as vector graphics in the page and the arithmetic runs in your browser, which is why it keeps working once the page has loaded even if your connection drops.

That architecture is also a privacy decision. Because nothing you do with the instrument is sent anywhere, there is nothing about your practice sessions for us to store, lose or hand over. The privacy policy sets out the small number of things the site does keep, all of them on your own device.

What it is not

The written guides

The simulator answers "what does this read?". The guides answer everything around it — where the least count comes from, why the vernier principle works at all, what each of the twelve parts is for, and which standards govern them.

• How to read a vernier caliper — The five steps, the TR = MSR + (VSR × LC) formula worked through, and the six mistakes that spoil a reading.
• Least count — Where 0.02 mm comes from, a table of every common vernier, and the four jobs a caliper is the wrong instrument for.
• Zero error — The fault that adds itself to every reading you take, why it is invisible in the results, and how to correct for it.
• Parts of a vernier caliper — All twelve parts named and explained, plus the ISO, ASME, BS and DIN standards that govern them.
• Frequently asked questions — Short answers to the questions that come up most often about reading and using a caliper.

Corrections and suggestions

The site is maintained by one person, and it is written carefully but not infallibly. If a worked example is wrong, a standard is out of date, or the instrument behaves in a way a real caliper would not, we would genuinely rather hear about it than not. Get in touch.