Discipline that pays.
ALWAYS WORK ON A COPY
Never on the only version of the source.
CHECK A TOTAL YOU ALREADY KNOW
Before trusting anything else.
USE TABLES
So formulas and ranges extend automatically.
SEPARATE DATA, CALCULATION AND OUTPUT
Onto different sheets.
DOCUMENT ON A NOTES SHEET
Where data came from, what you cleaned, what each calculation does.
NAME THINGS MEANINGFULLY
Sheets, files and named ranges.
AVOID HARD-CODED NUMBERS IN FORMULAS
Put the value in a cell and reference it.
Otherwise nobody can find it later.
PREFER SEVERAL SIMPLE STEPS
Over one formula nobody understands.
SAVE VERSIONS AT MILESTONES
So you can return to a working state.
CHECK ROW COUNTS AFTER ANY OPERATION
Records disappear silently.
REVIEW BEFORE SENDING
Hidden sheets, old data, personal information.
WHAT THESE PREVENT
The errors that produce confident wrong answers.
