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Trade mathematics and unit conversions · Lesson 3 of 4

Trade mathematics and unit conversions: methods and worked application

A seven-step method, then worked examples from decimal feet to the tape, a coping blank width, the 48 in sheet check, area and weight, a sloped edge, a 64 ft cut plan and thermal movement, each with its units and rounding written down.

You will be able to: Apply a seven-step documented method to tape readings, girth and Blank Width, sheet fit, weight, true length, pieces and billed length, and thermal movement, with units and rounding stated.

12 min · 11 slides · 9 questions

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Slide 1 of 11

A documented method in seven steps

The method has seven steps: write every dimension with its unit; convert to one working unit with exact factors; calculate without rounding; round once, by purpose.

Then check the AFS limits; sanity check by estimating first and reversing the answer; and record the work.

The tools do the arithmetic, not the thinking: you still choose the units, the rounding and the check.

A documented calculation, step by stepA flow from writing every dimension with its unit, converting with exact factors and calculating without rounding, to a decision on what the number is for, with three exits: round down for a fit limit, round up for an order or bill, nearest sixteenth for a shop mark; then check the limits, sanity check and record the work.Write every dimension with its unitConvert to one working unitExact factors: 25.4, 0.3048, 0.45359237Calculate without roundingWhat is thenumber for?Fit a limitround DOWNOrder or billround UPShop marknearest 1/16Check the limitspiece 126 in max, blank 48 in maxSanity checkestimate first, then reverse itRecord the workinputs, factors, rounding, tool

A flow from writing every dimension with its unit, converting with exact factors and calculating without rounding, to a decision on what the number is for with three exits (round down for a fit limit, round up for an order or bill, nearest sixteenth for a shop mark), then checking the limits, a sanity check and a record.

The seven steps of the method. The limits shown are AFS's: a piece of 126 in at most, and a blank of 48 in at most.

Sources

Videos for this lesson

What this video shows: A Khan Academy introduction to the Pythagorean theorem for the sides of a right triangle. Checked against the video's description, not its transcript.

Video: The Pythagorean theorem intro | Right triangles and trigonometry | Geometry | Khan Academy by Khan Academy, on YouTube. Chosen from the video's published description.

Glossary

Blank Width
FlashDraft's quoting figure for a profile: the sum of its flat legs measured to the sharp-corner (mold-line) lines, plus a hem allowance for each hem. It is not the shop's developed blank after bend deduction.
Hem allowance
The flat material a hem uses in the quoting girth. At the starting values an open hem adds 2 × 1/2 + 1/8 = 1-1/8 in, and a smashed hem adds 2 × 1/2 = 1 in.
Slope factor
The sloped length per unit of plan run, √(1 + (rise ÷ 12)²). At 6:12 it is 1.1180, so a 16 ft plan run is 17.889 ft of sloped metal.
True length and plan length
True length is the real length of a sloped line. Plan length is its horizontal projection, as seen from above, and is always shorter on a slope.
Linear foot (LF)
One foot of length along a run. AFS bills linear feet, rounded up, after an estimated 10 % allowance when no stock length is set.
Sanity check
A quick estimate made before the calculation, and a reverse calculation after it, to catch a slipped decimal or a wrong unit before the number is used.