Practical guides, how-tos and comparisons to get the most out of our free online tools.
Series adds, parallel adds reciprocals — that part is easy. The parts that catch people: which member dominates the answer, why two 5 % resistors in parallel are still 5 %, and why the smallest resistor in a parallel pair takes the largest share of the power.
Lena Hoffmann · 15 min read
The 40 % limit for three or more conductors is not about whether they physically fit. It is about heat and about pulling them in without stripping the insulation — and the moment you use that space, the code takes current away from every conductor in the pipe.
Marco Bianchi · 17 min read
Measured, not asserted: 90 short real phrases across six languages, none declined and 68 right — 76%, falling to 64% under sixteen letters. Four of the wrong answers came back at 100% confidence.
Daniel Okonkwo · 16 min read
Section area times length times density, for nine profiles and fourteen metals. What the calculator returns, why one figure covers every carbon-steel grade, and the two places its geometry is not the merchant's geometry.
Marco Bianchi · 13 min read
Blocks, base gravel, drainage stone, geogrid and pipe, counted from the calculator's own output. Then the number nobody puts in a materials list: a saturated backfill pushes about 2.2 times as hard as a drained one.
Marco Bianchi · 12 min read
Twice the centre distance plus both circumferences is 36 % too long. Here is the real formula, how the two straight runs and the two arcs actually add up, how far the standard approximation drifts, and what to do with a figure that is not a catalogue length.
Marco Bianchi · 15 min read
Torque does not hold a joint together — preload does, and torque is a poor proxy for it. Here is where 90 % of your effort goes, what the K-factor really is, and why the same 37.84 N·m gives anything from 12.61 kN to 37.84 kN of clamping force.
Marco Bianchi · 14 min read
01/02/2026 is 1 February in most of Europe and 2 January in the United States, and nothing in the string says which. ISO 8601 fixes that, sorts as text, and stops being ISO 8601 in four specific places that RFC 3339 rejects.
Daniel Okonkwo · 16 min read
A PDF carries its metadata twice, in two stores that can tell different stories, and neither of them is the whole story. Here is what is actually in the file, what clearing it removes, and the two things that survive every wipe.
Daniel Okonkwo · 15 min read
Numbering a tidy document is trivial. The cases that bite are a page turned sideways, a Letter sheet among A4 ones, a print file with bleed, and a document that already prints its own number. All four were tested: on the first three the number lands exactly where you asked, and the fourth is not detected at all.
Daniel Okonkwo · 14 min read
Bars each way, splice lengths in bar diameters, cover from the edge, and the exact tonnage to order. Run against the calculator, including the two places where its bar count comes out short.
Marco Bianchi · 12 min read
How to tell a sound secret-key generator from an unsound one, using this one as a worked example: which random source it calls, how to compute the entropy yourself, and what actually breaks the day you rotate the key.
Daniel Okonkwo · 13 min read