Course of business evidence shows routine practices can establish whether an act occurred under ordinary business procedures. The existence of a course of business by which an act would naturally have been done is a relevant fact to determine whether that act occurred. Established business routines may be used to infer specific occurrences: for example, ordinary practice of placing letters for posting combined with proof a letter was so placed bears on whether it was dispatched; proof a letter was posted in due course and not returned supports that it reached the addressee.