FORMULA SHELF
15 of 370
The arithmetic behind the work: what to measure, what to type in, and what the answer comes out as. Every formula says what the symbols mean and gives a worked example, so you can check it against a job you have already done.
SHELVES
Kitchen
3 formulas
A boiling thermometer is worth the money. Overcook the jam and it goes tough, undercook it and it runs. See Jam Jelly And Preserves.
Add 1% extra sugar and the set comes at about 62 C instead of 65 C.
The rules that decide what goes in the freezer. Label everything with the date and what it is.
A joint frozen for 12 months is still good, but it has lost its water and is better as a stew.
Lime makes the maize release its niacin, which is the whole point of treating it. See Flint Corn And Popcorn.
1 kg of maize and 1 L of water with 15 g of lime makes about 1.1 kg of nixtamal.
Agronomy
3 formulas
The rule that makes a heap work. Too much carbon and it sits there for a year; too little nitrogen and it goes sour and smells. See Compost Heap.
A heap of 100 kg straw at 80:1 needs about 2 kg of nitrogen, which is 4.5 kg of urea.
Grain dried too fast or too hot goes cracked, and the cracks cost you in the mill. See Storing Grain.
Wheat at 22% harvested to 15% stored, 8 t/ha: (22 - 15) x 8,000 / 100 = 560 kg of water a hectare.
The setting that goes on the drill. Work it out from the seed rate, then check it over a measured 10 m and count.
60 kg/ha of maize, 7,700 seeds/kg, rows 0.75 m apart = 104 seeds a metre.
Livestock
3 formulas
The single number that tells you if a ration or a system is working. Weigh the animals, do it again in 30 days, and divide.
A lamb goes from 30 kg to 42 kg in 60 days = 0.2 kg/day.
Measure it, and aim to get it under 380. A long interval usually means the cow is losing condition before the bull goes in.
Calved 15 March and 20 March the next year = 370 days.
Write the treatment date and the withdrawal date on the animal or in the book, and check the milk before it goes in the tank. See Vaccinating And Cold Chain.
Treated on 1 June with a 14-day withdrawal: nothing in the tank before 15 June.
Growing
1 formulas
A plant that goes out too early loses a fortnight. Harden it off properly and it will lose a week of growth instead of a month of plants.
Last frost 15 May: plant out the tomatoes from 27 May.
Workshop
3 formulas
Measure from the edge of the hole to the edge of the flange, not to where you think the bend goes. Add the allowance to the flat length before cutting.
A 10 mm radius bend at 90 degrees in steel: 1.57 x 10 = 15.7 mm of extra metal.
Water on a level yard is water that never leaves. Get the fall right with a laser level or a long spirit level and a pegged board. See Underground Pipe And Trenches.
A 20 m yard falling 1 in 80 drops 250 mm from end to end.
Concrete gains most of its strength in the first week. Keep it damp for the first three days and cover it if it is hot or frosty.
A gate post in concrete should stand for 48 hours before the gate goes on.
Chemistry
1 formulas
Each one holds the other two constant. A cold bottle warms in the sun and the pressure goes up, which is why a bottle left in a hot shed can go off.
Gas at 10 C in a bottle warms to 30 C and its pressure rises by about 7%.
Advanced maths
1 formulas
When one goes up and the other goes down: speed and time, men and days, pressure and volume.
Two pumps fill in 6 hours, four pumps in 3 hours.
SOURCES & PROVENANCE
1 listed
This page is an AI-organised index. The label means the grouping and cross-links were compiled with AI; the information itself comes from the public-domain books, reports and manuals listed below. Open any source to read the local copy or follow the link to the original publication.