DIRECTIONS: Answer question 1 in pen before you read the box.
Scissors only, with a grown-up in the room. If a step seems to want a knife, snip or fold instead.
What you need: a plastic bottle · a jar · scissors · tape · a ruler · card · small stones · a pencil.
A washing-up bowl and an egg cup are both left out in the same shower of rain. Which one ends up with deeper water in it?
Neither: the same. The bowl catches more, but spreads it over more floor, and the two cancel. So rain is measured as a depth, not an amount: half an inch in a thimble or a pool.
Test it. Put two straight-sided containers of very different widths out
in the next shower, away from the house. Measure the depth in each.
Why a Bottle Lies
Making · Projects · Page 2 of 6
DIRECTIONS: Cut the top off the bottle and turn it upside down into the base. Then read this.
A bottle does not have straight sides. Its dimpled bottom and curved shoulder make a ruler read wrong at both ends.
The fix is to move the nought.
1. Cut the bottle across the shoulder. Turn the top upside down and drop it into the base
— that is your funnel, and it is waterproof, which a card one would not be.
2. Drop a few small stones in the bottom so the wind cannot take it.
3. Pour water in until it is above the dimples and into the straight part, and the
stones are covered.
4. Mark that line. That is nought, not the bottom of the bottle.
5. Every reading from now on is measured up from that mark, and you empty back down to it
rather than emptying it out.
The page 3 strips tape on the outside, zero on your mark, on anything with a
straight middle.
Four Scales
Making · Projects · Page 3 of 6
DIRECTIONS: Cut out ONE (page 4 says which). Tape it on with the 0 line on your mark.
Funnel and collector the same width? Use ×1 (real inches). A wider funnel
makes the water climb faster: page 4 works out which strip.
Making It Read Bigger
Making · Projects · Page 4 of 6
DIRECTIONS: Measure across the widest part of the funnel’s mouth, through the center, then the collector.
Catch it wide, collect it narrow, and the reading grows, which makes small rain easy to read. It grows by the SQUARE of the widths: a funnel twice as wide reads four times as much; three times as wide, nine.
Funnel across
1.5 in
2 in
2.5 in
3 in
3.5 in
3 in
×4.0
×2.3
×1.4
×1.0
×0.7
3.5 in
×5.4
×3.1
×2.0
×1.4
×1.0
4 in
×7.1
×4.0
×2.6
×1.8
×1.3
4.5 in
×9.0
×5.1
×3.2
×2.3
×1.7
Round to the nearest strip on page 3. A two-liter bottle (4.2 in) into a jam
jar (2.6 in) gives 2.6: the ×3 strip under-reads by about a
seventh. Close enough for a garden.
Under ×1? Swap the funnel and collector. Over ×4? A storm
overflows it: use a wider jar.
Measure your own two and work out your number. Show the division and the squaring separately, so you can see which step did the work.
Where It Goes
Making · Projects · Page 5 of 6
DIRECTIONS: Pick the spot before you start. Moving it later spoils the log.
Do this
Because
Out in the open, well away from anything tall
At least twice as far away as the thing is high. A wall, a fence or a hedge makes a pocket of still air on one side and a gust on the other, and rain does not fall straight down through either.
Never under the eaves, a branch or a washing line
It will read nothing at all in a light shower and then get a fortnight’s worth in one drip when the gutter overflows.
Rim about a foot off the ground
Lower and rain bouncing off the ground splashes back INTO it. Higher and the wind starts carrying drops over the top instead of into it.
Rim level, and check it again after a windy night
A tilted mouth is a smaller mouth as far as falling rain is concerned, so it under-reads — and it will not tell you it is doing it.
The same spot every time
The whole value of a rain log is comparing one week with another. Move the gauge and you have started a new log.
Why twice the height away? Wind lifts over a wall and tumbles behind it, carrying rain to one side. Far enough away, it flattens out again.
The Log
Making · Projects · Page 6 of 6
DIRECTIONS: Read it at the same time every day, dry days too. Then empty it to your zero mark.
Date
Rain since yesterday
What the sky did
Add up a whole week. Now find out what the forecast said for that week, and compare. If they disagree, which do you trust, and why?
Did the heaviest day come with the darkest sky? Look down your two right-hand columns before you answer.