Max/Msp SuperDirt timing problem

arg… it’s not working at all, I don’t understand what I need to do precisely to achieve the scheduling. for the moment I compare the timestamp in the message with “real time ellapsed” between events. some of them are late, others are ahead of time (in my case I try with e ternary beat for the moment, s “bd bd bd”).
maybe counting the ellapsed time between events is not the best strategy? I’m lost, thank you for your help

Guillaume