[Dabhand16]

I've always metered with no filter first (or my trusty Western Master v) if using a graduated filter. If you meter with the filter on, surely it would not underexpose the sky (if you are using it that way up) and at the same time it would overexpose the foreground. (unless you had a really demon matrix exposure system that would cancel out the effect of the filter). The idea here is to correctly expose the foreground, but reduce the exposure the sky gets, thus bringing out more detail, or reducing the burn out.

ND's are a different kettle of fish. (not graduated ND's). If you meter with them off, the exposure will be under exposed. I thought tha idea with ND's was to allow you to use larger apatures/slower shutter speeds in bright conditions. You are effectively fooling the meter into 'thinking' there is less light than there actually is. The meter will correctly expose the scene which has had the dimmer applied to the sun!