The paper is an analysis of a personal diary with regard to the categories of continuity and discontinuity. Initially, the author considers not only two typical diary mediums: a notebook, which gives continuity to the subsequent notes, and loose pieces of paper, which - conversely - are a material sign of a diary's discontinuity, but also exceptional cases of continuity and discontinuity of notebook series or agenda notes. Then he points at the necessity of examination of a diary's rhythm, which is the frequency of notes additions (together with their length) in reference to historical time. He suggests his own, short definition of a diary as 'a series of dated traces'. In the following part of the paper he regards a diary as a kind of 'activity' and not a 'product', and discusses the reasons and the significance of the breaks in diary writing, i.e. the discontinuity of notes additions. Finally, the author presents two interesting diaries as regards time construction: by Pierre-Hyacinthe Azais (1766-1845) and Claude Mauriac (1914-1996). The former was writing his diary for 34 years in 366 different files and added the subsequent notes using the same date but a year before. The latter, after a few dozen of years of diary writing, started composing further volumes by contrasting his notes written in different periods. In this way, as distinct from Azais, Mauriac transgresses the chronological continuity of a typical diary.