The method 1, further comprising determining a third metric for a third process chamber of a third plurality of process chambers used to perform a third process step of {HEAD ~ said sequence} of interrelated process steps, wherein said third metric indicates a time to a third planned maintenance event for said third process chamber and wherein supply of substrates to said {TAIL ~ third plurality} of process chambers is controlled so as to synchronize said third planned maintenance event with said first and second planned maintenance event 
The method 1 , further comprising determining a third metric for a third process chamber of a third plurality of process chambers used to perform a third process step of { HEAD ~ said sequence } of interrelated process steps , wherein said third metric indicates a time to a third planned maintenance event for said third process chamber and wherein supply of substrates to said { TAIL ~ third plurality } of process chambers is controlled so as to synchronize said third planned maintenance event with said first and second planned maintenance event
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