Question: Procedure - Give Value of it

Good day,

Proc_-_Mapleprime.mw

I was wondering what goes wrong with the procedure I wrote.
I inserted a short example, otherwise I didn't know how to explain it.

When looking at the Maple sheet:
It concerns determining the eigenfrequency and then specify a factor to that eigenfrequency.
The first plot is the 'critical range expressed in FREQUENCIES'. I plotted this using a procedure.
Now in the second plot I converted the first plot, which is expressed in FREQUENCIES, to a certain critcal range in LENGTH.

Now my point is that I would like to view the reductiefactorvoetgangers(lengte) when I type in for example lengte:=22; but it gives an error. I don't understand why it does that.

In case of the first plot (expressed in FREQUENCIES), i can just simply fill in eigenfrequentiesysteem:=1.7 and then it gives me an answer for reductiefactorvoetgangerseigenfrequentie(eigenfrequentiesysteem) which is equal to 1 (which is correct).

So if anyone can tell me what I do wrong, I would appreciate.
Thank you

Greetings,
Frank