Ebay cheapy ones. Checked mine against accurate scales and they are accurate enough for salmon. I find it easier to weigh them in metric the convert to lbs and oz as digital scales like to give .1 of a lb rather than and oz.
I carry the Korum digital scales. Compact, not so light, but accurate. Of course that latter may not matter so much in salmon fishing Graham. I've caught any number of 1lb15oz roach and rudd: an ounce is a lot in that kind of fishing. But strangely I've seen very few salmon between 19.5lbs and 20lbs in the records of salmon fisheries I've visited.