Thanks! Now I understand. I even don't know the perpetual calendar is belong to the Lange 1 model.The weight of L1 Platinum is much heavier than the L1pc since my PC is YG.I don't have any problem to see the date,day,and month but the year is a bit too small for me. Honestly to say, I personly prefer the Datograph than PC. I think the layout of PC is a little bit too complicated. I like the Datograph layout.It's really beautiful. I used to collect the Patek Philippe but the Lange become my favorite recently!