i dont usually weigh fish unless they look big to me, trout until they get to 3 or 4 pounds i just measure length. the 15 pound scale in the link is similar to the older brass one i have, there are ones with finer graduations and one with 4 oz marks can be read to 2 oz if it falls between the lines, close enough for what i need from a fish scale.
http://www.chatillon.com/Our%20Products/Chatillon%20Weighing%20Scales/fish%26game_product/IN_fishscale.html