sequence instruction

What type of electromechanical switch does a sequence instruction replace?

Sequencer, Much like your Washing Machine Timer, It is not necesarily one Switch, most are made up of several or many switches, all set to operate a specific times or up specific indexed points.

Some washing machine timers have 6 seperate switches some activate at diferent times during different cycles, others operate at different times furing other cycles, and potentially many operate at the same time during even differnt cycles. It all depends on how it is set up.

Drum switch

dum, dum, dum, er...excuse me, I mean drum, drum, drum switch!

I remember siemens sequence software it basicaly had a rook of function block software where you could not find the sequence bits if not documented & was a load of B$%&**^, I converted one it was as simple as this
the original siemens concept was a function that if you set a flag (step is true it stepped on).
whats wrong with...
a input x
a input y
set next flag
reset last flag
& so on.
or...
create a counter register & set it to 1 at startup of sequence then increment it with the logic(suggest inc by 10 to allow a few extra steps you forgot later on)
then if you need to go back to a step you force the counter to the step you want.
simple.....