Give every counter one component
Associate each reading with exactly one engine, generator or unit. “Port engine” and “starboard engine” are more reliable than one shared engine-hours field.
Treat readings as a time series
Store the value, time and author. New values must not overwrite prior readings. Reversals can indicate errors, replacement or repairs and need explanation.
Document meter replacement
Record the final old value, first new value, date and reason. A calculated lifetime total can be maintained separately.
Link maintenance to the actual reading
Capture the counter when work is completed so the next due point derives from the real completion rather than an estimate.