What do you mean by police diary? When can a Magistrate, police officer and accused person make its use?

The investigating police officer shall day by day enter his proceedings in the investigation in the police-diary, setting forth therein the time and date of receipt of the information, the time, date and place of beginning and closing of the investigation and details of the facts and circumstances of the case.

Any criminal Court may sent for the police diaries of a case under inquiry or trial in such Court, and may use such diaries, not as evidence in the case, but to aid it in such inquiry or trial.

Neither the accused not his agents shall be entitled to call for such diaries, nor shall he/they be entitled to see them merely because they are referred to by the Court; but, if they are used by the police officer who made them to refresh his memory, or if the Court uses them for contradicting such police officer, the provisions of Section 161 or Section 145, Indian Evidence Act, 1872, shall apply. [Section 172, Criminal Procedure Code, 1973]