Why are there two aggregations used for Consumer ID?

Hi Julianne,
thanks for reaching out! That's a great question.
When we use COUNT we allow to have repeats - in this case repeat consumer IDs in the purchase table, which means that even if a consumer has placed two or three distinct orders, we'll count each occasion.
When we use COUNTD we count only the number of unique IDs, meaning that no matter how many purchases an individual has made, we'll only count one of them, as it is the only distinct purchase.
To the calculate the frequency of orders for our chart we want the total number of orders made by all consumers, divided by the distinct orders by each customer. In other words we count once all the consumer IDs, where we can have repeat IDs or repeat purchases, and then we factor in the distinct consumer IDs to observe the ratio between all purchases and the number of purchases made by each distinct consumer.
Hope this helps!

Best,
365 Eli