Keeping a reading log that is worth reading later

Why most journals are unusable
The standard reading journal records the cards drawn and how the reader felt. Six months later it supports no conclusions, because it contains no prediction that could have failed.
A log becomes useful the moment it records a claim with a date attached.
The five fields
Question, verbatim. Written before the draw, not reconstructed after.
Spread and positions. Named positions, in order, so the reading can be re-derived.
Cards, in the order drawn. Not rearranged.
The reading, in one or two sentences. Declarative. No hedging.
The check date. A specific date on which you will return and record what actually happened.
A reading you cannot be wrong about is a reading you cannot learn from.
Reviewing
Review monthly, not continuously. Read only entries whose check date has passed, and mark each one as confirmed, disconfirmed, or unresolvable. The unresolvable pile is the diagnostic one: a large unresolvable pile means the questions were unanswerable, not that the cards were unclear.
What the numbers are for
Rates matter less than patterns. Most practitioners find that specific card-position combinations are consistently over-read in their own practice, and the log is the only way to find out which.
Keeping it short
Five fields, under a hundred words per entry. A log that takes fifteen minutes per reading will be abandoned within a month, and an abandoned log teaches nothing.