Question about DH parameters

Please see image on this link:

Why is it that d1=152? Based on my understanding it should be d2. As I understand d2 should be measured from origin of previous frame which is x1 z1 origin measured to intersection with x2 along z1 axis. Based on the illustration d2 should be 152 then why is it on d1? Is there something wrong with my understanding?

THank you very much for answers.

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