Combo f stop deduction/increase

[crotograph]

If I were using, say, Fuji NPH on a foggy, rainy or overcast day (say ISO 400) and, to remove the bluish cast that occurs when the sky is overcast, I was also using an 81a filter, what would the proper stop down/increase calculation be? The recommended f stop increase for the 81a filter is 1/3 stop and the film latitude is 4-5 stops with a 1 or 1/2 stop deduction for f/ss when metering for shadow. What would the overall filter and latitude deduction be? Would I calculate the deduction first and then add the 1/3 stop back in or is there a rule of thumb calculation I could use to achieve proper exposure?

Math reasoning has never been a strong point and any sunshine on this would be appreciated.

[another view]

First off, I'd say that NPH has a higher latitude than that. There are different schools of thought on how to do this, too. I usually overexposed neg films, maybe by 2/3 of a stop so this would be ISO250. The printing process should easily be able to duplicate the effect of an 81A or even 81B filter during printing (and they can just as easily negate it too). I guess I wouldn't worry about an 81A unless you're shooting chromes. I'm not sure what you mean by "f/ss".

What's the most important part of the shot? If you're shooting people, then I'd get the exposure on them right and let the latitude of the film pick up whatever it can in the background. I might use fill flash to close the gap between the background exposure (outdoors) and the exposure of the subject. If you're shooting landscape, I usually prefer a spot meter and pick a couple of things to meter - basing my exposure on what's most important in the shot.

[crotograph]

Understood AV, just wondering whether there was a general rule of thumb for calcs.