Group delay plot of a Moving average filter

Question

I am implementing the moving average filter in Matlab. Using fvtool on this filter, gave the following output curve, is this group delay curve correct?

Edit:

My confusion is regarding the values of the delay output as well as the constant nature of the curve.

I implemented the filter using 'FilterDesigner' tool in matlab
(In which, filter dimensions can be specified in the GUI, which then handles the code itself) Attaching a screenshot of the tool window with filter parameters.

After which I exported this filter as an object called 'Hd'

To plot the filter, I did -
fvtool(Hd)

Which resulted in the curve above (figure 1)

Matt L. · Answer

You could have added to your question why you doubt the correctness of those numbers. Anyway, the group delay of a moving average is indeed constant. It's just the parameter 'window size' that is off by one. The window size $N$ is the number of taps of the moving average filter, and the group delay is related to the window size by
$$tau_g=frac{N-1}{2}$$
However, in your plot, the group delay is half of the window size, so I expect that what is called 'window size' actually equals $N-1$, i.e., the number of taps minus $1$.

Group delay plot of a Moving average filter

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