Now that I have work on timing belt after whatch lots of related vide os. The people made the videos didn't show clearly what the marks look like and how to find them, I start this thread to help next person whom want to working on timing belt:
Mark on cams sprockets: I don't know about other models, but the marks on my 07 XC70 are very difficult to see, after turned the engine several turn and couldn't fine them, I consulted the forums, Iran accross a thread said he have to run his finger nail on the sprocket to find the mark, went out tto the car, turn the engine with one hand, while run my finger naile of other hand on the cam sprocket (not easy for an over sixty years old guy recovered from a stroke). Finally my finger naile cought on the mark, still hard to see after I found it; It's as thin as a hair, indented about 1mm long on the edge of the sprocket, do the same to find the one on other sprocket!!!
Mark on crankshaft sprocket: Many pictures on youtube, but look down to the crankshaft sprocket you really don't see any on the teeth, it's right behind the hamonic balancer (crankshaft pulley), again turn the engine with one hand (I'm get used to it now) run other hand finger on thething(?) between the end of sprocket and the hamonic balancer, it had three long rised, find a small rised one, after you touch it, shine the flash light behind the hamonic balancer, now you see the mark!!