I just do this, from the Kodak Portra Technical data sheet http://imaging.kodakalaris.com/sites...portra_400.pdf
, except I usually add a stop of extra exposure for insurance (so in sun I'll do F8 1/1000). I do the same same for Trix. but I also judge by vision for shadows and clouds, backlit subjects, etc. I always wear sunglasses in daytime, so I have learned to judge light with those particular sunglasses. If I ever lose them, I'll have to learn light over again.
Bright or Hazy Sun on Light Sand or
Bright or Hazy Sun (Distinct
Weak, Hazy Sun
Heavy Overcast or Open Shade‡ 1/500