Numbers stored as text break SUM, lookups and sorting. Spot them in seconds, then convert with Convert to Number, Paste Special, Text to Columns, VALUE/NUMBERVALUE or Power Query, plus the hard cases.
TRIM leaves spaces behind? Find out exactly which character it is with one formula, then remove non-breaking spaces (CHAR 160), line breaks, tabs and zero-width characters in Excel or Google Sheets.
ARRAYFORMULA, MAP/LAMBDA or fill down in Google Sheets? A decision table and side-by-side formulas for row math, AND/OR per row, row totals, running totals and per-row SUMIFS.
COUNTIF, COUNTIFS or SUMPRODUCT? A decision table plus tested examples for AND, OR, case-sensitive, row-by-row and month counts, and the edge cases that give wrong totals.
FILTER or QUERY in Google Sheets? A decision table, 9 side-by-side formulas, and the traps (mixed data types, case, column letters, empty results) that decide which one to use.
Calculate hours worked in Excel when a shift crosses midnight. Copy the MOD formula, subtract breaks, total over 24 hours, split night hours and overtime. Free timesheet.
SUMIFS returns 0 when you give one column two criteria. Sum North OR West with an array constant, a criteria list, FILTER or SUMPRODUCT, without double counting.
VLOOKUP returning the wrong value in Excel or Google Sheets? Fix the missing FALSE argument first, then check duplicates, column numbers, relative ranges and wildcards.