A maintenance log is the accumulated history of what has actually been done to a machine, and almost every site keeps one badly for the same reason: the log is written to prove that work happened rather than to inform the next decision. Those are different documents. A log that proves work happened needs a date, an asset and a signature. A log that informs the next decision needs what was found and how long it took, and those are precisely the two fields that get skipped when somebody is filling it in at the end of a shift. This page is about the second kind of log and what it lets you do.
Record what was found, in words, every time
'PM completed' is a tick. 'PM completed, coupling insert showing wear, replaced, second time this year' is the sentence that changes an interval and justifies a spare. If a log has no findings in it after a year, either the plant is remarkable or the log is not being used for anything.
Record hours, because the schedule is priced in hours
On the worked example this site publishes, the schedule is 66 technician hours a month and the reactive work is 193.2 avoidable hours. Neither figure exists without durations in the log, and durations recorded as 'morning' cannot be added up.
Keep it against the asset, not against the visit
A log entry that covers three machines is unreadable later, when the question is about one of them. This is the same discipline as one work order per asset and it is the thing that makes a two-year-old log answerable.
Read it once a year, per asset
The annual review is what the log is for: checks that never find anything, faults that keep recurring between checks, and assets whose entries are getting longer. Nobody does this and it is the highest-value hour in the maintenance year.
Questions people ask about maintenance log
Paper or digital?
Either, as long as somebody can answer a question about one asset across two years without opening a filing cabinet. That is the real test, and it is where paper eventually fails.
How long should logs be kept?
For plant with statutory inspections, whatever your regulator requires, which is often longer than you would guess. For everything else, long enough to see two or three intervals, so at least three years.
Who writes the log?
The person who did the work, at the time. A log compiled later by somebody else is a summary, and summaries lose exactly the incidental detail that turns out to matter.