advance/retard unit

[CBNelly]

Hello Everyone
Enjoying working on my 400/4 in the sun setting up the carbs and timing
I've had the advance/retard unit in bits and now back together and on the bike
However I've come across a 0.1mm thick shim (23mm OD x 15mm ID) on my workbench and wondered if I missed during the reassembly
Does anyone have a photo breakdown of the unit?
Thanks

[CBNelly]

Think I've answered my own question!!
Found a spare unit (or two) in by box of spare parts
Shim seems to sit under the central sleeve!!