The way you understood LOD's are bit different.
Its true that the LOD's are not affected by other dimension filters but you need to understand that the dimension filters do filter out the dimension on which you calculated your LOD.
To understand this, looking at your example at a carrier name level instead of aggregate.
LOD Delays on Carrier Name level and you can see the grandtotal using average matches with what you have
Comparing the same with avg delays without any LOD calculation
Since there is no other dimension, other than carrier name (on which your LOD is calculated), both the calculations will match exactly same.
But once we introduce airport name as a filter, we will see a considerable difference
You can see that the values from LOD calculation stays the same but the other calculation differs as per the airport selection.
The statement "FIXED calculations are applied before dimension filters, so unless you promote the fields on your Filter shelf to Improve View Performance with Context Filters, they will be ignored." means the calculations are dependent only on the dimensions used in the LOD calculations. But this doesn't mean the dimension filters do not affect the no.of dimensions in the view and thus affecting overall averages.
Hope this helps.
In your case, you need create another calculation for average of each carrier as shown below
an updated workbook attached for your reference.
Hope this helps
Flights_v10.2.twbx 337.4 KB
Jeevan's answer is correct. They key is that the FIXED LOD is being calculated first, on all the data, and then part of the data is filtered out when the viz is constructed.
It's helpful to look at this page, to see what order things are done in.
To correct your issue, right-click on your filters in the Filter shelf and select "Add to Context". Context filters are applied before FIXED LODs are calculated.
Thanks a lot for your beautiful explanation. You were right that I had not understood how LOD expressions work exactly especially FIXED which is more common than others. The dimensions are also an important thing to take into account when we are using the same in our calculation.
It was just a couple of Tableau users whom I work with had confused me into believing that no matter what LOD Fixed will never change by the introduction of dimensions in filters or the view.
If there was a better official explanation about the same topic in the official Tableau documentation with the right examples then Tableau users will not get so confused. But luckily we have this Tableau Community Forum where we can help each other when in need.
Coming to the figure of 2438 with just the Carriers and 2840 with Airport Name on the filter shelf. It makes sense why the number changes because there are 3 carriers Alaska, Hawaiian and Virgin which do not fly to Baltimore/Washington International Airport.
Thank you for the answer and that was a clever trick to use FIXED calculation again to show the same number on the view without having to add the filter to the context.
Thank you for your answer. I did use the Context filter work around to get the right figure which I was after. The only thing confused me was the work around with LOD Calculations, Order of Operations Logic and Dimension Filters. Now everything is clear for me.