Custom field with value of total updates to another field
I have a custom date field, which I am able to update via the API - let's call it field_a.
This works fine. However, I need a custom number field_b to record the number of times field_a has been updated (for the relavent contact).
I looked at https://bit.ly/2ZCYVSb but could not find what I needed.
Can you suggest a way to achieve what I need?