Practical guides, how-tos and comparisons to get the most out of our free online tools.
Epley, Brzycki, Lombardi, O'Conner and Wathan are five curves through the same data. They agree within a few pounds at low reps and disagree by a quarter at fifteen — which is exactly how you know when an estimate is worth having.
Aisha Karim · 14 min read
Work out exactly how many months a savings goal will take from your monthly deposit, starting balance and interest rate — with worked examples.
Camille Laurent · 4 min read
The denominator should be delivered, not sent — which means defining hard and soft bounces properly. Unique and total opens are different numbers. And a reported open rate has a computable null point: past a certain share of prefetching clients it carries no information about humans at all. The instrumentation that replaces it.
Camille Laurent · 12 min read
SWOLF adds seconds to strokes, which is dimensionally indefensible and useful anyway. The catch is what it rewards: it prices one stroke at exactly one second, so it can improve while you get slower — and it is not comparable between pools of different lengths.
Aisha Karim · 12 min read
Your bid decides whether you are eligible; the advertiser below you decides what you pay. Doubling a bid can move the price not at all, quality can halve it for the same position, and the average CPC in your report is a click-weighted mixture that describes no query. The auction arithmetic, worked.
Camille Laurent · 13 min read
A slug has two jobs that pull against each other: it is a permanent identifier and it is a piece of readable text. Length, hyphens, stop words, dates, non-ASCII characters and the identifier-plus-slug pattern that gets both properties — with the real numbers from a site that localises 1,736 tool slugs into six languages.
Camille Laurent · 13 min read
Rolling resistance grows with speed, air resistance grows with its square, and power grows with its cube. Work the equation and the crossover falls at 10 mph — after which almost everything you pay for is air, and a headwind costs more than the same tailwind returns.
Aisha Karim · 12 min read
Naismith's 1892 rule times a route in two lines of arithmetic. It also ignores descent completely and assumes a fit walker with no pack. Here is the rule, Langmuir's fix, and Tobler's continuous alternative — whose fastest speed is on a downhill, not on the flat.
Aisha Karim · 12 min read
Maximal aerobic speed is the slowest speed at which you reach your VO2max. Because it is a speed and not a heart rate, every training zone becomes a percentage of something you can measure on a track — and the whole week falls out of one test.
Aisha Karim · 12 min read
Find the weekday of any birth date. Learn the quick calculator method and a short introduction to the Doomsday rule for working it out in your head.
Lena Hoffmann · 4 min read
Understand how a subnet mask splits an IP address into network and host parts, what /24 means, and how to count usable hosts.
Daniel Okonkwo · 4 min read
Count the weeks between today and any future date. Learn the simple divide-by-seven method, when to round, and the difference between inclusive and exclusive counting.
Lena Hoffmann · 4 min read