How to make it: Cut the top third off a straight-sided plastic bottle, invert that top and fit it into the bottom part — it becomes the collecting funnel. Stick a strip of paper marked in millimetres along the side of the lower part (or use a ruler), starting from the inside base. Put a few pebbles at the bottom outside the measuring line, or set the bottle in a weighted tin, so wind cannot topple it.
Rules that decide whether your readings are worth anything:
- Open ground, away from trees, walls and the edge of a roof — anything overhead steals or adds rain.
- Flat, level surface; the mouth of the gauge must be horizontal.
- Read at the same clock time every day, then empty the gauge.
- Record ‘0’ on a dry day — a blank is not the same as a zero.
- Let snow or hail melt before measuring.
Sample answer (a month during the monsoon):
| Week | Daily readings (mm) | Total (mm) | Average per day (mm) |
|---|---|---|---|
| Week 1 | 0, 0, 12, 4, 0, 8, 4 | 28 | 28 ÷ 7 = 4.0 |
| Week 2 | 15, 22, 30, 18, 6, 0, 7 | 98 | 98 ÷ 7 = 14.0 |
| Week 3 | 2, 0, 0, 5, 11, 3, 0 | 21 | 21 ÷ 7 = 3.0 |
| Week 4 | 0, 9, 26, 34, 12, 5, 0 | 86 | 86 ÷ 7 = 12.3 |
Average per week = 233 ÷ 4 = 58.25 mm
Comment on the variation: The rain did not arrive evenly. Weeks 2 and 4 gave over four-fifths of the month's total, while Weeks 1 and 3 were nearly dry. Rain in India comes in spells, not in a steady drizzle — a few days of active monsoon, then a break of a week, then another spell.