The question is as to the date of A's birth. An entry in the diary of a deceased surgeon, regularly…

Section 26(b) makes relevant a statement of a deceased person made in the ordinary course of business, especially an entry in books kept in that course or in the discharge of professional duty. Illustration (b) to section 26 declares the deceased surgeon's diary entry relevant on A's date of birth, so the answer is "A relevant fact, as a statement of a deceased person made in the ordinary course of business". The diary need not be a public record.