TechRef

The drawing says 50.000 +0.200 / -0.000. The number you set on the machine is 50.100. TechRef does that calculation, and converts to every unit at the same time. 【WHY THE CENTER VALUE MATTERS】 The center of an asymmetric tolerance isn't the drawing's nominal dimension. TechRef calculates the true center and tolerance band, so the first setup is right. Input: 50.000 +0.200 / -0.000 Center: 50.100 Range: 50.000 – 50.200 mm 50.1000 (50.0000 – 50.2000) in 1.9724 (1.9686 – 1.9763) 【LOOK UP TOLERANCES FROM A STANDARD】 (TechRef Pro) Pick an ISO 2768 class (f, m, c, v) or an ISO 286 fit (H7, g6–p6), and TechRef looks up the deviations for the size you entered — no need to calculate by hand. Choose H7 for a 50 mm bore: Upper deviation: +0.025 Lower deviation: 0 Center value: 50.0125 Change the size or unit and it re-checks the class, converting inches to mm first. Name classes ISO or JIS (ISO 2768-m / JIS B 0405-m) — same values. 【INCH DRAWINGS, METRIC MACHINE】 Working between inch drawings and metric equipment: enter in inches, read in mm; enter a tolerance in thousandths of an inch, read the band in microns. 【SHOW ONLY THE UNITS YOU USE】 12 categories — Length, Area, Volume, Weight, Temperature, Energy, Angle, Time, Force, Pressure, Power, Speed — over 100 units in total. Choose exactly which units appear — from just mm and inches, up to bar, atm, mmHg, kgf/cm², knots, Mach, BTU, or metric horsepower. Traditional Japanese units (尺,寸,坪,合,升,斗,石,匁,貫) are included, plus rice-trade weights 俵 and 石 (1 俵 = 60 kg). Conversion factors come from defining values, never a truncated approximation. 【ROUNDING THAT ERRS ON THE SAFE SIDE】 Tolerance bands round inward, lower limit up and upper limit down, so the displayed band is never wider than the true one. If rounding would collapse a narrow band, TechRef adds decimal places instead. 【INSPECTION SHEETS】 Create a sheet per part, add measurement points, and give each a dimension and tolerance. Categories can share a part — this one in length, that one in weight. Copy as CSV to the clipboard, or save to Files. One row per point, ready for Excel or Numbers. 【TAP DRILL SIZE TABLES】 (TechRef Pro) Metric (coarse M1–M48, fine M8×1–M48×3), Unified (UNC/UNF/UNEF, #0–2 in), and Whitworth (BSW, 1/16–2 in), each with the thread's tolerance range so a drill on hand can be checked. Checked against a Japanese tap maker's JIS chart, size by size; unverified sizes aren't included — fewer rows, not an unsafe one. 【TOLERANCE TABLES BUILT IN】 (TechRef Pro) General tolerances (ISO 2768: linear, chamfer, and angle — three tables) and fits (ISO 286: hole H7, shafts g6 to p6, up to 500 mm). JIS B 0405 and JIS B 0401 are officially identical to these ISO standards, so tables also show under JIS names. Choose which classes and sizes appear. 【DRILL SIZE TABLES】 All three systems — number (#80–#1), letter (A–Z), fractional (1/64–1 in) — with inch and mm. Browse by system, or a combined table sorted by size. The Use button sends any value straight to the converter, where you can add a tolerance. Tables search by name, standard, or term. 【FREE, AND TECHREF PRO】 Conversions, manual tolerance calculations, the drill size tables, viewing history and sheets, and CSV export are all free and unlimited. Free saves are limited; past the limit, once per hour. TechRef Pro (a one-time purchase) unlocks unlimited saves, the tap drill and tolerance tables, and standard tolerance lookup. Not a subscription. 【EVERYTHING STAYS ON YOUR DEVICE】 No server. TechRef works fully offline — useful with no signal on the shop floor, essential for confidential dimensions. No ads. No tracking. No analytics SDK. No account. History and sheets are files on your device, never sent anywhere. 【ALSO INCLUDED】 • Searchable history with labels, notes, and standard classes • 1–6 decimal places • Copy selected rows with one tap • Larger text sizes (Dynamic Type) • Light/dark appearance, iPhone and iPad