I'd say new spring scales would be fine, but they don't stay new enough. In one of my last tournaments I was half way through one day culling. It seemed all my bass weighed the same nearly, making it tough to decide. After about 3 culls one apparent 2.5# bass of all 2-2.5# bass caught suddenly clicked down to 3#. It happened again, especially when jerking the scale up a little. I guess it had a rough spot from rust or some impact damage.
When doing fisheries work we had both, a spring scale and a very expensive digital scale. The accuracy of both matched, but like Keith wrote, the spring scale can't give you ounce increments, not being a precise instrument, though probably very accurate if you could just read ounces. Like also said, those ounces sure can make the difference. The digital scale was of course a lab quality model costing a couple thousand bucks. Very accurate and precise to 1/10,000 oz. Someone up the ladder decided we didn't need such precision, so the expensive one was replaced with a Rapala digital scale. It was good to 1/10 ounce and a lot more convenient. We tested it against the lab model and found the accuracy right on.
How many tournament fish have you seen weighed on a spring scale? Probably never in the last ten years. There is no guessing, no interpolating between spring scale divisions. The accuracy of digital is simply unbeatable. I carry two different brand digitals, Berkley and Rapala, both always agreeing, one at the bow, the other at the console. The bow scale hangs by the hook from a Go-To bait holder under a compartment lid. The other hangs from an access hole inside the console.
Jim