PMP Certification - How do I prove the amount of PM hours that I have put in?

I am a BA. As part of my job I have carried out PM tasks for about 16 months. I have not yet applied to become a member of PMI or for the exam. Questions: - Can my experience before I join PMI count toward the 4500 hours of PM time? - How do you work out the hours? - How do I prove that I have done the 4500... show more I am a BA. As part of my job I have carried out PM tasks for about 16 months. I have not yet applied to become a member of PMI or for the exam.

Questions:
- Can my experience before I join PMI count toward the 4500 hours of PM time?
- How do you work out the hours?
- How do I prove that I have done the 4500 hours?
- Do I have to get something signed by my manager?
- What if I can't get it off my previous manager as I have left the company?
- Can you do the exam and then finish obtaining the 4500 hours before getting the certification?
- I heard some people say about writing up the experience. What does that entail?

I have seen lots about taking the exam, but not a lot about proving the 4500 hours put in.

Many thanks.
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