Digital scales are Ok for big carp .
Not true.
Some scales are very inaccurate. Some are slightly. Some are always accurate.
That goes for digital or analogue.
The general rule of thumb is always going to be, like everything else, you get what you pay for.
First off, if you want to find an accurate set, take a known weight with you and test the different scales on offer.
This isn't foolproof, but it might weed out some obvious rubbish.
Second, always tension the scales with a sling (or something with at least a few ounces weight), then zero.
As Records Officer for a specimen group, I use Salter Electro-Samson Digitals.
They weigh in 1/2 ounce divisions as well as grammes, require one battery which will last for several years average use (unlike Fox Digis), and they are always spot on. I test them twice a year at a scales shop a few doors down from my work.
They're light, compact, rugged and picked up for £35/45 new if you shop around. I've never had a problem with the display under any environmental conditions (e.g. snow, rain, ice, frost etc).
I wouldn't use anything else.
And many of the group now use them, too.