COSESAI

The A/B Test Verdict: When “Significant” Isn’t the Whole Story

By xiezixing 2026年7月15日

A single p-value is not a decision. Here are the three numbers — p-value, lift, confidence interval — that turn a dashboard spike into a verdict you can defend, plus how Bonferroni and sequential-testing corrections keep multiple A/B tests honest.

Audio Frequency Analyzer: five-band spectrum display

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Five Bands, Twenty Hertz to Twenty Kilohertz: How to Read an Audio Frequency Analyzer

By xiezixing 2026年7月14日

A spectrum analyzer turns your ears into a screen you can defend in a mix review. Here is what the five-band display actually tells you — and the three traps that make it lie.

Entropy Calculator poster — Shannon, Min-Entropy, Strong/Medium/Weak rating and CPU-vs-GPU cracking times for sample inputs

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Measuring Cryptographic Strength with an Entropy Calculator

By xiezixing 2026年7月14日

Length is not a security metric. Use Min-Entropy to measure how unpredictable a password, key, or token really is — and how long it would take an adversary with 10⁶ to 10¹² guesses/sec to crack it.

Dice Probability Calculator cover with title and stats row

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Why Dice Probability Doesn’t Behave the Way Your Gut Says

By xiezixing 2026年7月14日

Two six-sided dice have 36 ordered outcomes. Sum 7 hits 1/6 of the time. The triangular histogram is your mental model for craps, Yahtzee, Catan robber rolls, and every D&D attack roll.

CRC32 Checksum tool — IEEE 802.3 32-bit fingerprint for ZIP, PNG, gzip, and Ethernet integrity

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The 32-bit Fingerprint Your Computer Uses a Billion Times a Day: A CRC32 Field Guide

By xiezixing 2026年7月14日

CRC32 is not a hash. It is the cheapest integrity check in computing, and the reason ZIP, PNG, gzip, and Ethernet all know when something went wrong.

Significant Figures Sandbox — 5 rules, 3 modes, 4 traps mental model

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Five Rules That Decide Whether Your Measurement Is Honest: The Significant Figures Sandbox

By xiezixing 2026年7月14日

Count, round, and propagate significant figures with a sandbox that grades each digit and walks you through the rules — built for chemistry and physics students who keep getting 0.005030 wrong.

SEDOL validation explained with seven characters one check digit and a weighted mod 10 control

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Seven Characters, One Check Digit: Catch a Bad SEDOL Before It Reaches Your Books

By xiezixing 2026年7月13日

A practical guide to SEDOL-7 format rules, weighted mod-10 validation, and where securities-data pipelines should catch a bad identifier.

Markdown Link Extractor cover image showing link inventory workflow

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Before You Crawl Your Docs, Inventory the Links in the Markdown

By xiezixing 2026年7月13日

Five link forms, two reference passes, and a five-stage audit walk-through for the Markdown Link Extractor on Elysia Tools.

Chat Transcript to PDF — cover poster showing JSON to bubble PDF conversion with stats row

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Chat Transcript to PDF: How to Turn JSON Conversations into Bubble-Style Documents

By xiezixing 2026年7月13日

A working walkthrough of the Chat Transcript to PDF tool — JSON input shape, five layout switches, three raw-transcript pitfalls, and how it sits among the rest of the document-conversion family.

Regex Linter — five regex risk categories, four rewrite rules, one pre-commit gate

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The Regex That Hangs Your Server at 3 a.m. — A Pre-Commit Guide

By xiezixing 2026年7月13日

Five catastrophic-backtracking categories, four mechanical rewrites, and a 60-second pre-commit check that beats every ReDoS post-mortem.

The A/B Test Verdict: When “Significant” Isn’t the Whole Story

Five Bands, Twenty Hertz to Twenty Kilohertz: How to Read an Audio Frequency Analyzer

Measuring Cryptographic Strength with an Entropy Calculator

Why Dice Probability Doesn’t Behave the Way Your Gut Says

The 32-bit Fingerprint Your Computer Uses a Billion Times a Day: A CRC32 Field Guide

Five Rules That Decide Whether Your Measurement Is Honest: The Significant Figures Sandbox

Seven Characters, One Check Digit: Catch a Bad SEDOL Before It Reaches Your Books

Before You Crawl Your Docs, Inventory the Links in the Markdown

Chat Transcript to PDF: How to Turn JSON Conversations into Bubble-Style Documents

The Regex That Hangs Your Server at 3 a.m. — A Pre-Commit Guide

Boolean Algebra Simplifier Field Guide: When Four Literals Collapse to One Gate and a Karnaugh Map Proves It

Z85 and RFC 1924 Base85 Field Guide: When Four Bytes, Five Characters, and Two Alphabets Decide Whether Your Payload Survives the Wire

Image Steganography Field Guide: When Three LSBs and One Chi-Square Number Tell You Whether the Message Is There

APNG IDAT/fdAT Chunk, Streaming Deflate Replay and Disposal Method Frame-Timing Analyzer Field Guide: When Three Chunks and a Hundredth of a Second Decide Whether Your Animation Ships