Anc*y has this record
UK, Royal Hospital, Chelsea: Regimental Registers of Pensioners, 1713-1882
Alexander McKayBirth Place
Reay, Caithness occ
LabourerRank Sergeant
Regiment 79th Foot
Regimental Number 327
Age at enlistment 18
Attestation Date 28 Jun 1823Attestation Place Thurso, Caithness
Document Type Soldier's Service Documents
some info. from
Detailed Statement of Services of No 327 Sergeant Alex ‘r McKay
Private 1st Jan 1829 to 31st Dec 1832
Promoted
Corporal 1st Jan 1833 to 24th March 1835
Sergeant 25th Mary 1835 to 7th Oct 184
9 edit should read 1844
edit to add
From Detailed Statement of Services of No 327 Sergeant Alex ‘r McKay
5ft 10, dark hair, eyes black, complexion dark, trade a labourer
and
Opinion of medical officer at Dublin?
November 21st
1844Sgt. Alexander McKay having this day been examined by medical board, at Dublin? of which I was President, has been found unfit for further service from,

in both legs, also rheum...? & general debility
Added on the first page it says
he served abroad six years in
Canada six years