A remembered glance is difficult to compare with last month. A dated record lets you distinguish “the left rear tyre is lower again” from “the tyres seem fine”. Record the conditions and units as well as the reading.
A monthly review can help you notice recurring problems; it is not permission to wait a month before checking the vehicle. The Highway Code advises weekly tyre-pressure and fluid checks; follow the vehicle handbook, pre-journey needs and any warning sooner. The examples below let you practise interpreting checks without needing access to a vehicle.