Commenting here (a good opportunity) on counting methods for any technical reader ... the enumeration approach I take (and encourage) is to count all human passengers, including under-5s. Babies yet to be born are not counted, however - "this is my last week before I go off on maternity", regrettably, was just a count of one. Staff at work are not counted, employees of the railway travelling in the passenger accommodation and not working are counted (sometimes, of course, we can't tell). Dogs and other pets are not counted. The person counting is only counted if he / she is travelling for purposes other than the count - i.e. would have been on the train anyway.
Having checked grahame's counting methodology above, I submit this count for the 1147 from Westbury on 12th August:
Westbury 6
Trowbridge 15 (9 boarding)
Melksham 25 (11 boarding/1 leaving)
Chippenham 17 (8 boarding/16 leaving)