I recently had an experience with a client where she used many small pieces of paper to record her 'to do' items. It became apparent that sooner or later the wheels would fall because pieces of paper can quickly be lost.

It is advisable to ONLY USE ONE DIARY and ONE CALENDAR as then everything is in one place and there isn't guess work about where it is. Then keep all these in a central place and when you have finished using something, put it back in that central place.