hay @crokkon and thanks for the review and feedback.

I did use (active_users_at_the_beginning - active_users_at_the_end) / active_users_at_the_beginning to calculate the churn

"Churn = Number of Active users at the beginning of the period + New registrations – Number of Active users at the end of the period.

Churn rate can be calculated using

Churn rate = Churn / Number of Active users at the beginning of the period."

The problem with the weekly and negative churn is down to steemit inc not creating accounts at the same pace each week. the variance on the week to week is to much to make sense really.