Articles
Reference guides and explainers on investing, software, genetics, and the apps.
Investing
Common Sources of Error in Trading Backtests
The issues that quietly make a backtest look better than the real thing.
The Wash-Sale Rule and Finding a Replacement
Sell the loss, keep the exposure, stay out of trouble. The 61-day window, what 'substantially identical' means, and how people actually pick a substitute.
Beta vs Correlation: Two Numbers People Keep Confusing
One says how closely things move together. The other says how far. Measured values for real securities show why the difference matters.
Reading a Form 4: Which Insider Trades Mean Anything
Most filed transactions are not decisions. The code letter tells you which ones are — and open-market buying is under a tenth of the total.
Dollar-Cost Averaging: The Case For and the Case Against
Buying at fixed intervals lowers your average cost per share. It also, on average, lowers your return — both are true.
Risk-Adjusted Returns: The Arithmetic and the Catch
Sharpe, Sortino and the ratios built on them — what each divides by, and why a high one is not a recommendation.
Rebalancing: What It Costs and What It Buys
Selling what went up to buy what went down. The arithmetic, the tax bill, and why calendar rules beat instinct.
Index Funds and ETFs: What Actually Differs
Three S&P 500 funds track at 0.999 to each other. Since the exposure is identical, the decision is about everything else.
Compound Interest, and the Two Things That Break It
The formula, the Rule of 72, and why the real-world result is always below the projection.
Asset Allocation: Correlation Does the Work
Diversification is not owning many things. It is owning things that do not move together — which is measurable.
Order Types: What Each One Guarantees
A market order guarantees execution, a limit order guarantees price. No order type guarantees both, and that is the whole subject.
Volatility, and What the Number Actually Tells You
The arithmetic behind the figure, measured values for real securities, and the two readings people get wrong.
Development
UUIDs: Which Version to Use, and Why v4 Is Usually Wrong for a Primary Key
The versions that matter, the collision maths, and the index fragmentation nobody warns you about.
Base64: What It Is For, and the 33% You Pay
Not encryption, not compression. A way to move binary through channels that only accept text — at a measurable cost.
Hashing: Which Algorithm for Which Job
Checksums, digital signatures and password storage need three different families. Using one for another is how breaches happen.
JWTs: What They Prove, and the Mistakes That Undo It
Signed, not encrypted. Readable by anyone holding one, and hard to revoke — which decides where they belong.
Cron: The Five Fields, and What Bites in Production
The syntax takes ten minutes. The environment, the overlap and the missing hour take longer.
JSON: The Spec Is Small, the Edge Cases Are Not
Numbers that lose precision, duplicate keys, and why you cannot store a date.
URL Encoding: Which Function, and Where
Different parts of a URL have different rules. Using one escaping function everywhere is how links break.
Regular Expressions: The Parts Worth Knowing
Greedy versus lazy, capture groups, and the catastrophic backtracking that takes a server down.
Unix Time: Seconds Since 1970, and Where It Goes Wrong
Leap seconds, the 2038 problem, milliseconds versus seconds, and why a timestamp alone is not a time.
HEX, RGB, HSL and the Colours You Cannot Mix in Them
Why #808080 is not half as bright as white, and why HSL lightness lies about lightness.
Character Encoding: Why Text Arrives Broken
Mojibake, the BOM, and why a string's length depends on what you mean by a character.
Genetics
Reading a Raw DNA File: The Format and Its Limits
Four columns, several hundred thousand rows, and a set of things the file genuinely cannot tell you.
SNPs: What a Single Letter Change Does and Does Not Mean
rs numbers, odds ratios, and why 'associated with' is doing far more work than it looks.
Genotype and Phenotype: Why the Genes Do Not Settle It
Dominance, penetrance and expressivity — the reasons two people with the same variant differ.
DNA, Genes and Chromosomes: How the Pieces Fit
Two metres of DNA in every cell, 20,000 genes, and the 98% that does not code for protein.
Genetic Deep Dive Report
399 SNP variants across 23 categories.
Apps
DeadSpread, and Why Jam Bands Are Archived Like No Other Music
An app for the Grateful Dead, Widespread Panic and the wider scene — built around a recording culture that has no real parallel.
legitWeather, and How to Read a Forecast Properly
Current conditions, hourly and daily forecasts, a map and saved locations — plus what a 30% chance of rain actually means.
KOCaffeine: Keeping a Mac Awake, Precisely
A keep-alive utility for macOS with fine-grained control over exactly when the machine stays up.
Klaar: Removing macOS Apps and What They Leave Behind
Dragging an app to the Trash removes the app. Klaar removes the rest of it — including developer toolchains.
Mac App Store or Direct Download: What the Choice Decides
Sandboxing, updates and notarisation — and why one of these two utilities could not ship through the store.