Guides
Deep dives by topic: formulas, assumptions, common mistakes and worked examples.
Hiragana vs Katakana
Usage, shapes and learning order.
指南 · GuideSpaced Repetition and the Forgetting Curve
1/3/7/14/30/60/120-day intervals and daily planning.
指南 · GuideOn Readings vs Kun Readings
Where the two reading systems come from and when they appear.
指南 · GuideAn N5 Kanji Study Order
From numbers and nature to people, school and transport.
指南 · GuideHow to Study N4 Kanji
By theme, with vocabulary, and by distinguishing similar characters.
指南 · GuideFrom N5 to N4
Kana, N5 kanji, N4 kanji, vocabulary and grammar.
指南 · GuideA Plan for N4 Vocabulary
Themes, collocations, examples and output.
指南 · GuideThe Full N4 Path
Kana, N5, N4 kanji, N4 vocabulary, grammar and reading.
指南 · GuideHow to Study N4 Grammar
Connections, examples, contrasts and output.
指南 · GuideWhere N4 Grammar Fits
The order of kana, kanji, vocabulary, grammar and reading.
指南 · GuideAn IELTS Vocabulary Plan That Sticks
High-frequency words, examples, spaced review and output practice.
指南 · GuideUsing Academic Words in Writing
Collocations, word forms, examples and avoiding word salad.
指南 · GuideSpanish Pronunciation Basics
Five vowels, stress, ñ and common consonants.
指南 · GuideA 60-Word Spanish Plan
Ten words a day, examples, review and output.
指南 · GuideWhat to Learn First in Python
Variables, containers, control flow, functions and modules in order.
指南 · GuideCommon Python Traps
Mutable defaults, shallow copies, integer division, is vs ==.
指南 · GuideDaily Git Workflow
The status, diff, add, commit, pull and push loop.
指南 · GuideUndo and Recover in Git
Choosing between restore, reset, revert and reflog.
指南 · GuideExcel Formula Basics
References, absolute/relative, errors and IF.
指南 · GuideVLOOKUP, XLOOKUP and INDEX+MATCH
When to use each lookup and common errors.
指南 · GuideThe Word/PPT Shortcuts Worth Learning
Save, undo, formatting, slideshow and alignment.
指南 · GuideA Keyboard-First Presentation Workflow
From new file and layout to slideshow, using keys.
指南 · GuideMental Math Strategies
Rounding, splitting, times tables and exact division shortcuts.
指南 · GuideTimes Tables That Stick
From 2/5/10 to 7/8/9, practiced on a forgetting curve.
指南 · GuideSQL SELECT Basics: WHERE, ORDER, LIMIT
The minimal query structure for filtering, sorting and limiting rows.
指南 · GuideSQL JOIN and GROUP BY
Joining two tables, aggregate groups and HAVING.
指南 · GuideHow to Read Python Output
Expressions, repr, operator precedence and common traps.
指南 · GuideList and Dict Output: Slices, Comprehensions, get
Slice bounds, list comprehensions, dict keys and get defaults.
指南 · GuideHow to Read JavaScript Output
Operators, coercion, truthiness and JSON formatting.
指南 · GuideReading map, filter and reduce
What array methods return, callback arguments and chaining.
指南 · GuideRegex Basics: Classes, Quantifiers, Anchors
\d, \w, +, *, ?, ^, $ and escaping.
指南 · GuideGroups, Greediness and Lookaround
(), (?:), greedy/non-greedy and (?=)/(?<=).
指南 · GuideTenses and Subject-Verb Agreement
Present/past, perfect tenses and third-person singular.
指南 · GuideArticles, Prepositions and Passive Voice
a/an/the, collocations and was/were + past participle.
指南 · GuideLearning English, French and Spanish Together
Main language, maintenance language and cognate strategy.
指南 · GuideCognates and False Friends
Similar-looking words in English, French and Spanish: when to guess and when not to.
指南 · GuideHow to Read the Periodic Table
Periods, groups, atomic number and atomic mass.
指南 · GuideIons and Isotopes
Charges, electron gain/loss and neutron counting.
指南 · GuideRemembering Countries and Capitals
Group by region, locate on a map and learn English names.
指南 · GuideRegions, Currencies and ISO Codes
Regions, three-letter currency codes and two-letter country codes.
指南 · GuidePhysics Formulas and Units
Formulas and units for speed, density, force, work, power and pressure.
指南 · GuideOhm's Law and Electric Power
U=IR, P=UI, series/parallel and units.
指南 · GuideArea and Perimeter Formulas
Rectangles, squares, triangles, circles and trapezoids.
指南 · GuideVolume and Surface Area Formulas
Cuboids, cylinders, spheres and cones.
指南 · GuideSpanish Regular Verb Endings
-ar/-er/-ir endings across five tenses.
指南 · GuideUsing Five Spanish Tenses
When to use present, preterite, imperfect, future and conditional.
指南 · GuideFrench Regular Verb Endings
-er/-ir/-re endings in present, imperfect, future and conditional.
指南 · GuideUsing Five French Tenses
Present, imperfect, future, conditional and passé composé.
指南 · GuideSolving Linear Equations
Transposition, like terms, brackets and checking.
指南 · GuideQuadratics and Systems
Factoring, two roots and elimination.
指南 · GuideItalian Regular Verb Endings
-are/-ere/-ire endings in present, imperfect, future and conditional.
指南 · GuideUsing Four Italian Tenses
When to use present, imperfect, future and conditional.
指南 · GuideCountry Codes and Calling Codes
ISO alpha-2/alpha-3, ccTLDs and dialing codes.
指南 · GuideTimezones and Border Counts
Timezone counts, land borders and island countries.
指南 · GuideMean, Median and Mode
Calculating and choosing the three measures of center.
指南 · GuideVariance and Standard Deviation
Population variance, sample variance and standard deviation.
指南 · GuideSimple and Compound Interest
The difference between I=Prt and A=P(1+r)^t.
指南 · GuideROI, Gross Margin and Break-Even
Denominators and meanings of three common business metrics.
指南 · GuideClassical Probability and Urns
Favorable over total outcomes, with and without replacement.
指南 · GuideCoins, Dice and Cards
Binomial coins, 36 dice outcomes and 52 cards.
指南 · GuideVLOOKUP and INDEX/MATCH
Lookup column, return column and exact match.
指南 · GuideText, Date and Logic Functions
LEFT/MID/TRIM, YEAR/MONTH/DAY and IF/AND/OR.
指南 · GuideAdding and Subtracting Fractions
Common denominators, numerator operations and reduction.
指南 · GuideMultiplying and Dividing Fractions
Multiply numerators, divide by multiplying the reciprocal and reduce.
指南 · GuideSimplifying and Solving Ratios
GCD, cross multiplication and the basic property of proportions.
指南 · GuideDirect, Inverse and Proportional Sharing
y=kx, xy=k and sharing by parts.
指南 · GuideSQL JOIN Types and Usage
INNER/LEFT JOIN, join conditions and aggregation.
指南 · GuideSubqueries, EXISTS and Window Functions
IN/EXISTS, correlated subqueries and ROW_NUMBER.
指南 · GuideQuestion Tags and Conditionals
Positive/negative tags, three conditional types and tense pairing.
指南 · GuidePassive, Relative Clauses, Gerund/Infinitive
Be + past participle, relative pronoun choice and verb patterns.
指南 · GuideDerivative Rules
Power rule, constants, sums/differences and second derivatives.
指南 · GuideDefinite Integrals and Limits
Antiderivatives, bounds and canceling for limits.
指南 · GuideLiquidity and Solvency Ratios
Short-term liquidity and long-term leverage denominators.
指南 · GuideProfitability and Turnover Ratios
Denominators for profitability and asset efficiency.
指南 · GuideDebit and Credit Basics
Increase/decrease directions for assets, expenses, liabilities, revenue and equity.
指南 · GuideCommon Accounting Entries
Purchases, sales, loans, payroll, depreciation and investment.
指南 · GuideCounting Protons, Neutrons and Electrons
Atomic number, mass number, electrons and isotopes.
指南 · GuideIons and Isotopes in Atomic Structure
Charge, electron counts and isotope notation.
指南 · Guide