Practical guides, how-tos and comparisons to get the most out of our free online tools.
The usual rule — delegate whenever you earn more per hour than the help costs — is wrong, and wrong in a way that has a formula. Two thresholds, one for a household task and one for a business task, and the ratio between them is exactly one over one minus your marginal rate.
Camille Laurent · 15 min read
The received wisdom is that the tax treatment of depreciation settles the buy-or-lease question. Modelled on a 60,000-euro machine over five years, it does not: it ranks third, and a long way behind. Here is the ranking, computed, and the conditions under which it flips.
Camille Laurent · 15 min read
Chronological age is exact. Biological age is not one thing but three — epigenetic clocks, blood-marker scores and lifestyle quizzes — and only the first two have published validation. Here is how to tell which one you are looking at.
Sofia Nunes · 6 min read
Everyone runs this calculation forwards, from a rate to an income. Run backwards, from a salary to a rate, it produces a much larger number — on the 2026 French figures, 2.29 times the answer people reach by dividing. Here is the arithmetic, every subtraction named, in France, Germany and Spain.
Camille Laurent · 12 min read
There is a formula, and it is short: your living needs plus the company's fixed annual cost divided by the rate spread. That is why the answer is a threshold and not a preference — and why the threshold sits in four very different places in France, Germany, Spain and Italy in 2026.
Camille Laurent · 19 min read
There is no single towing capacity. There are four or five separate limits, and the one that binds is rarely the tow rating on the brochure — it is usually the vehicle's own weight budget, quietly consumed by the people sitting in it.
Marco Bianchi · 16 min read
WHO puts abdominal obesity at a ratio of 0.90 or more for men and 0.85 or more for women. But measuring in the wrong place changes the answer more than the threshold does — here is exactly where the tape goes.
Sofia Nunes · 6 min read
Removing tags and sanitising HTML are two different jobs. One real fragment run through a naive regex and through a formatting-aware stripper, with script and style contents, block breaks, comments, CDATA and entity order all shown as output.
Daniel Okonkwo · 14 min read
Engine rpm reaches the road through one unbroken multiplication chain, and the last link is the tyre. Change the tyre's rolling circumference and the speedometer goes wrong by exactly that percentage — in a direction the law cares about.
Marco Bianchi · 15 min read
Total stopping distance is two distances added together, and they follow different laws — one grows with speed, the other with speed squared. That single fact explains why doubling your speed roughly triples the distance.
Marco Bianchi · 17 min read
A compost heap wants 25 to 30 parts carbon to one part nitrogen by dry weight. Cardboard is 350:1, grass clippings 17:1. Here is the materials table, one mix worked through to 28:1, and why the volume rule of thumb is a different measurement entirely.
Marco Bianchi · 8 min read
A 13 by 17 ft room is 221 square feet of floor, but carpet comes off a 12 or 15 ft roll, so you buy 255 square feet and bin 34. Here is how to work out the order quantity your supplier will actually invoice.
Marco Bianchi · 8 min read