Guides
The calculators give you a number. These are the write-ups behind them — how the measurement is actually taken, where the error really comes from, and the cases where the obvious method gives a confidently wrong answer. Written from shop-floor practice rather than textbook order.
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How to measure roll length without unwinding it
Diameter math, weight, and counting wraps — what each method costs you in accuracy, and the one measurement that ruins all three.
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Reading a tank dip chart without fooling yourself
Why a horizontal tank's middle is so unforgiving, and the corrections — tilt, dished ends, temperature, water bottoms — that quietly cost you volume.
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Dilution math that survives contact with the shop floor
C1V1 = C2V2 is the easy part. The percent-basis trap, when density is required, why serial beats single-step, and the acid-into-water rule.
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Why alcohol plus water is less than the sum of its parts
Mixing ethanol and water loses up to 3.6% of the volume. What that does to a blend aimed at a target ABV, and how to work around it.
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Baumé, Brix and API: reading an old hydrometer
Four scales, four industries, and two of them aren't even the same formula. What 20° Baumé on a drum of muriatic acid actually means, and how to convert.
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Bleach dilution ratios: what 1:10 and 1:50 really mean
A ratio without a percentage attached is a guess wearing a number. The arithmetic that turns 1:10 or "1/3 cup per gallon" into an actual ppm figure.
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Diluting strong acids safely on the shop floor
The rule everyone half-remembers is acid into water. The arithmetic behind why it exists, how much heat you're really dealing with, and disposal basics.
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How to build a tank strapping chart by hand
Tape, measure, and prove a depth-to-volume chart for a real tank instead of trusting the drawing — with a worked example showing why the middle isn't halfway.
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Reading an electricity bill: kWh, rates, and appliance cost
A kWh figure on a bill and a wattage stamped on a tool look like one multiplication apart. Usually they aren't — duty cycles, tiers, and phantom loads.
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Why density tables say 20°C (and when to correct)
A hydrometer reading and a reference table only agree at the same temperature. How big the gap gets, and a fast way to decide whether it's worth chasing.
How we check what we publish, and how corrections are handled, is set out in our methodology.