Older types without digital engine control need manual synchronisation. One type I flew had a 'Syncrotac' which had three little wheelts for engines 2,3 and 4. If all wheels were staionary, these three engines were sychronised with engine 1.
Nimrod MR2 has this. Did the Comet 4 on which that aeroplane is based have it? The Comet has Avons while the Nimrod has Speys (which are said to be turbofans, but to me they look like hi-bypass turbojets).