FORMULA SHELF
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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
Agronomy
2 formulas
Every sprayer book starts with this. Get the volume right and the dose per hectare is right. Measure a nozzle with a jug, and time the pass over 100 m.
A 2 L/min nozzle at 8 km/h on a 6 m boom: (2 x 600) / (8 x 6) = 250 L/ha.
Catch the output from one nozzle for one minute to get flow. Measure your forward speed and the nozzle spacing on the boom. This tells you how many litres per hectare you are putting down, so you can mix the right amount of chemical in the tank.
1.5 L/min x 600 / (8 km/h x 0.5 m) = 225 L/ha.
Convenience only. Double-check the result against the worked example or a second method before you use it.
Workshop
4 formulas
Friction and heat are the losses. A lower efficiency means more fuel, more electricity and more heat to shift away.
A 1 kW motor driving a 400 W pump is 40% efficient, which means something is rubbing.
Whether you are rebuilding a gearbox, a mixer or a seedling thinner. Work it out on paper before you order the gears.
A 16 tooth pinion driving a 48 tooth gear is a 3:1 reduction.
For ordering felt, tiles, battens and underlay. Always order the underlay and never skimp on it.
A 10 m x 6 m building at a pitch of 0.7: 60 x 1.22 = 73 m2 a slope, so 147 m2 for both.
The difference between a saw that cuts along the grain and one that cuts across it. A rip saw has few deep teeth; a crosscut saw has many fine ones.
A 3/32 in gullet gives 1 / (2 x 0.094) = 5.3 TPI, a rip saw.
Energy
2 formulas
For sizing a solar array for the electric fence, the lights or a small freezer. Multiply the panel area by the irradiance you can count on, not the best case.
2 m2 of panel at 800 W/m2 and 20% gives 320 W.
How many units of heat you get for each unit of electricity. A COP of 3.5 means the heat pump heats three and a half times more than the resistance heater it replaced.
A 500 W heat pump with a COP of 3.5 gives 1,750 W of heat.
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.