Read a Value Off a Chart: Gridlines, Ticks and °F/°C

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Opens on Chapter 2’s example: the Millbrook river chart: a point three-quarters of the way from the 4 ft gridline to the 6 ft one.

Between two gridlines

Lower gridline

Upper gridline

How far up the gap a fraction, or measured height ÷ gap

Or: measured height above the lower line pixels or mm

…and the gap between the lines same units

What one tick is worth

One label

The next label

Ticks between them

Ticks counted up from the first label

A temperature axis

°F

°C fill one

Enter your numbers, then press Calculate.

How it works

A value between gridlines is the lower label plus the fraction of the gap times the gap: 4 + 0.75 × 2 = 5.5. A tick is worth the gap between two labels divided by the number of ticks between them, so never assume a tick is 1 or 100. Celsius is (°F − 32) × 5 ÷ 9.

From the book, Chapter 2. The river point reads 5.5 ft. Ticks of 250 make three and a half ticks above 1,000 read 1,875; assuming 100 a tick would give 1,350. 68°F is 20°C and 86°F is 30°C. Every chapter and its calculator →

Rounding is half up, the way the book rounds. Numbers can be typed as 1,450, $38, 12% or 2.5 million. Everything stays in your browser: no sign-up, nothing stored or sent.