Decoding the identifying reference

Each image comes with a unique six-part identifying reference code that is appended to the on-screen caption.

Example (as above): med_1971_col_02_010_18

Here's how it decodes:

#1: med - Meadows, Daniel identifies me as the photographer.

#2: 1971 - Date, the year when the image was made.

#3: col - Three letters describing a particular period or project. 

Codes used include:
col = college, student work, 1970-73
bus = Free Photographic Omnibus 1973-74
air = artist-in-residence, Pendle Lancashire, 1975-77
fre = freelance 1977-2000
gtv = Granada Television 1978-80
atv = Associated Television 1981
atn = And The North 1983
sub = Suburbia 1984-86
nat = now and then 1995-2000
mov = movie stills

#4: 02 - A two digit number referencing the precise file of negatives and contact sheets as archived, as here: College 02, Sep 1971-Mar 1972 

#5: 010 - A three digit number referencing the precise sheet of negatives, together with its corresponding contact sheet, as filed in the folder at #4 above.
Note: the negative sheet/contact sheet number is expressed by the first two digits, the third digit (frequently zero as here) is reserved for those occasional rolls of film which extend beyond one bag of negatives, where the first bag is labelled 'a' and the second bag 'b' e.g. med_1980_fre_20_24b_27

#6: 18 - The precise frame number on the sheet of negatives as embedded in the celluloid.