Mental estimation techniques

Landmarks before arithmetic

Place the number against a landmark you already trust: 0, a halfway point, a round ten, a known total. A journey of 47 kilometres is just under 50. A wait of 47 minutes is a little under an hour. The landmark does the first cut. The adjustment does the rest.

Compatible numbers

Replace the figures with neighbours that divide cleanly, calculate, then say which way you nudged. 19% of 248 is close to 20% of 250. Twenty percent of 250 is 50. Both nudges were upward, so the true value sits a little under 50. The exact product is 47.12.

That percentage is one case of compatible numbers. It is not the only kind of estimate Pinpoint is being designed around. A count, a distance, a duration, or a mark on a line can be the question instead.

A linear number line

On a line from 0 to 100, equal distances are equal values. The middle is 50. 62 sits twelve units past that middle, toward 100. People often compress or stretch one end of the line. The correction is to measure from a landmark, not to stare at the blank space.

Number-line estimation is an established research task. Two5 did not invent it. The papers below review that task and everyday quantity estimation. They are not studies of Pinpoint.

What a closer guess does not prove

Practising a puzzle makes you more fluent at that kind of puzzle. It does not establish a gain in general intelligence, or in performance outside the skill being practised.

Questions