I'm an eejit. I always wondered what that filter did. I have experimented with it a wee bit this morning and now I know. Thanks Stu.
One observation, when you quit WeatherCat and restart it, that filter defaults at startup to state that it is Off, but the slider is in the maximum position. However, the slider itself does not actually match up with the amount of filtering until you slide it all the way to the left and actually turn it off. After that, the slider matches the amount of filtering. If you don't do that after a restart, the filter says that it is off, but it actually defaults to the last setting in which you left it.
Again, thanks Stu.