I have created a Calculated metric for a particular dimension using the function approximate distinct count. but the dimension count and the calculated metric do not match. jus wanted to check the reasons behind the same.
Here when we use the Approximate Distinct Count there can be an accuracy with 0-5% mismatch error as the adobe uses Hyper Log -log Algorithm which can be accurate but have light mismatch. So this is pretty common when we use the Approximate distinct count.
Hope this helps
Please refer the link for your reference: https://experienceleague.adobe.com/docs/analytics-learn/tutorials/components/calculated-metrics/appr...
The other thing that can happen sometimes is that Multiple UVs can fall under "Unspecified"..
So users without an ID would all roll up to a single row (not saying that is the case here), but that can lead to difference in the other direction.