Hi
if the main date is the transaction_date do like this:
users:
Load [user_id],
[login],
[user_date_register],
...
from ....
transactions:
load [transaction_id],
[user_id],
[transaction_date] as Date,
[sum]
from ....
then in the chart put in the dimension Date
and in the expression put:
count([user_id]) as count_of_users
count([transaction_id]) as count_of_transactions
count([user_id])/count([transaction_id])
BR
Ariel
