"This value must be real." message when inserting chart components

You just forgot to use the "Vectrization operator", that's all you need to add to fix the problem!

Of course you should use km instead of just m when you divide KP and chose a different scale at the ordinate axis (highest value for example 4000 or let the Chart component select it automatically).

You are using a vector (KP) as argument for a function (F_fr) which expects a scalar argument (KP is finally used as limit of integration which must be a scalar). That's the reason for the error and that's what vectorization (the arrow over the expression) is made for 😉

You can find the "vectorization" operator either in the 'Operators' menu or use the keyboard shortcut Ctrl+Shift+6

I am not sure but If you still see the far too tiny font size and too small line width (as seen partly in the screenshots above) when you open the sheet you may have to open the Chart component and close it again to get rid of them. Reason is that I use a small notebook screen with a high 4K resolution and therfore a large Windows scale. The Chart component unfortunately is implemented in a rather amateurish way (also in other respects) and can't deal with that. This and because the component is far too slow reacting makes it unusable for me.

Prime 9 sheet attached