Set Analysis Reference Line Average

[Mitch_Data]

Hi

I have a set analysis as written below:

Count({$<[Datum - Verkoopdatum]
= {">=$(=Date(MonthStart(AddMonths(Max([Datum - Verkoopdatum]),-12)), 'YYYY-MM-DD'))<=$(=num(Year(Addmonths(Today(),-1))))-$(=num(Month(Addmonths(Today(),-1)),'00'))-$(=num(Day(Monthend(Today(),-1))))"}
,[Kenteken soort (grijs/geel)] = {'Geel'}, Brandstoffen -= {'Gas'}
>}[Auto volgnummer])

It gives the number of sales from 01-05-2021 till 31-05-2022, based on set analysis expression.

So Kenteken (License Plate) must be Yellow, Brandstoffen (fuel) must not be Gas.

Now I would like three reference lines. That average the other three fuel categories (Diesel, Petrol, Elektricity).

So basically I want the average count of sales per category fuel over 1 year.

My dimension is Year/Month sales and Fuel it looks like this

I want something like this, please do not be impressed by my paint skills:

Many thanks!

[Mitch_Data]

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