Practical guides, how-tos and comparisons to get the most out of our free online tools.
Re = ρvL/μ compares inertia with viscosity, and the units really do cancel. See the number worked out for honey, a household pipe, an artery, a swimmer and a wing — and why the 2 300 threshold belongs to pipe flow alone.
Lena Hoffmann · 9 min read
A full schedule from feeding the starter to slicing the loaf, and the one variable that moves every time on it. Five hours of bulk at 75 °F becomes about seven and a quarter at 68 °F.
Marco Bianchi · 6 min read
Hooke's law says force is proportional to stretch — but only below the elastic limit. Here is F = kx with worked numbers, what a 200 N/m spring actually feels like, and how springs combine.
Lena Hoffmann · 8 min read
The upward force equals the weight of the fluid pushed aside. That one sentence decides whether something floats, and if it floats, exactly how much of it stays under.
Lena Hoffmann · 6 min read
Three formulas cover the whole of projectile motion on level ground. The catch is level ground: the moment launch and landing heights differ, the 45° result stops being true.
Lena Hoffmann · 6 min read
Five variables, four equations, and each equation is missing exactly one of them. Choose by looking at the variable the question never mentions.
Lena Hoffmann · 7 min read
Cap rate is net operating income divided by price — a return that deliberately ignores your mortgage. Here is how to compute it, and why a high one is a warning as often as a bargain.
Camille Laurent · 4 min read
Rent minus charges minus the loan. On an 80 percent mortgage at 3.5 percent over 25 years, a rental only breaks even from about 7.1 percent gross yield — here is the full calculation.
Camille Laurent · 5 min read
Most of what buyers call notary fees is tax, not the notary. Here is the breakdown on a EUR 250,000 purchase and why an older home costs three times more to transfer than a new one.
Camille Laurent · 4 min read
Sample size is set by your baseline conversion rate and the relative lift you want to detect — and it explodes as that lift shrinks. Here is the formula, a full table at a 3% baseline, and why stopping early breaks the test.
Camille Laurent · 12 min read
CPM and CPC are not two prices for the same thing. They are the same auction seen from two sides, and click-through rate is the exchange rate between them — so the cheaper option flips as soon as CTR moves.
Camille Laurent · 12 min read
A photo file carries coordinates, an exact timestamp, the device and lens, and on some cameras a serial number. Here is what is actually in the block, what stripping does and does not fix, and how to verify it worked.
Daniel Okonkwo · 13 min read