Practical guides, how-tos and comparisons to get the most out of our free online tools.
Drawing your name onto a PDF produces a simple electronic signature. European law says that cannot be dismissed just for being electronic — and also that it carries none of the presumptions a qualified signature does. Knowing which tier you have is the difference between a document that holds and one you have to defend.
Camille Laurent · 9 min read
MD5 is broken and MD5 is fine, depending on which of three security properties you needed. Here is what collision resistance, second-preimage resistance and preimage resistance actually mean, which algorithm still has which, and why none of them belongs near a password.
Daniel Okonkwo · 15 min read
A character is three different things at once. One emoji with a skin tone is 1 grapheme, 2 code points and 4 UTF-16 units. Every count in this guide was measured in Node, plus why an SMS drops from 160 to 70 and why VARCHAR(255) is not 255 of anything in particular.
Daniel Okonkwo · 11 min read
10-20-10 does not mean 10 percent phosphorus. The second and third numbers are oxides, so a 50 lb bag holds 4.4 lb of actual phosphorus, not 10. Here is what each number really measures and how to turn it into a rate.
Marco Bianchi · 6 min read
Nobody owns a scanner any more, so the phone does it. Two things decide whether the result is accepted: how you took the photograph, and what page size it becomes. The second one surprises people, because a photograph turned into a PDF is not A4 unless something makes it A4.
Daniel Okonkwo · 9 min read
Flesch Reading Ease and Flesch-Kincaid Grade Level count syllables and sentence length. Nothing else. Both formulas in full, one passage scored end to end, and the comma trick that buys 3.9 grade levels without changing a word.
Daniel Okonkwo · 11 min read
A 110 in rise divided by a 7 in target gives 15.7 risers. You round to 16 and divide again, landing on 6 7/8 in. Here is the whole method, and why the building codes do not agree with each other.
Marco Bianchi · 7 min read
Marketplaces, job boards and support forms often accept JPEG and PNG and nothing else. Converting is easy; choosing the resolution is the part that decides whether the recipient can read your document, and it is the part every tool asks you about and nobody explains.
Daniel Okonkwo · 9 min read
A rental file, a loan application, a tender: the requester wants one document, in the order they listed. The merge itself takes seconds. What goes wrong is the ordering, the page sizes and the file that silently loses its signature — all of which are avoidable if you know where they bite.
Daniel Okonkwo · 10 min read
For sound, f' = f(v + v_o)/(v − v_s) — and getting the signs backwards is the classic error. Here is the convention spelled out, a 440 Hz source computed at four speeds, and why light needs a different equation entirely.
Lena Hoffmann · 8 min read
An HbA1c of 7 percent corresponds to an average glucose of about 154 mg/dL, or 8.5 mmol/L, or 53 mmol/mol. Here is the whole table, the formulas behind it, and when the number cannot be trusted.
Sofia Nunes · 4 min read
The first pass takes 30% off and the second takes nothing. That is not a broken tool — it is the difference between removing redundancy and removing information, and knowing which one you are doing tells you when to stop and what a second attempt actually costs.
Daniel Okonkwo · 10 min read