I've been using an Ohaus triple beam balance for 15 years. For determining jig weight in fractions of an oz. make yourself a chart showing gram conversions for your typical oz weights - 1/64, 1/32, 1/16 etc. Then when you weigh a jighead in grams, pick the nearest oz. weight to the gram weight.
Or to determine a 1/ weight, eg. 1/8, 1/10 etc. divide 28.35 by the gram weight. the result would be the bottom # of the 1/.
For lighter jig heads, it might be more accurate to weigh 10 together and divide by 10 to get individual weight.
Then again, maybe a digital postal or jewelers scale might be more economical.