I have several powder scales, a digital RCBS Chargemaster Auto dispensing scale, an Ohaus 1010 I bought when I was in college, and my Dad's old oil dampened Redding. I seldom use the RCBS because I don't think it is much faster than just using my Ohaus Duo-Measure and the Ohaus 1010 scale. The Ohaus scale has worked flawlessly for decades, and the magnetic dampening settles the beam quickly. It never needs batteries, and I expect it will outlast me. Set up is quick, and once set up, it never loses zero. I keep it covered and stored in the original box when not in use, and make sure the knives and agate bearings are free of dust. I see powder scales at gun shows that show rough use and abuse, and shake my head, because an accurate scale is probably the most important tool in reloading.
Any powder scale whether digital or balance type may be sensitive to air movement. Balance scale pans typically hang from a single point on the end of the beam. With digitals, it is important to center the load or pan over the correct spot on the tray. As Dustin said, digital scales do require a warm up period, and may still drift from zero. Before replacing your Dillon digital, it might be worth cleaning the battery terminals and trying a fresh set of batteries. And if it has a 110 volt power supply, it would be worth trying to use that to see if is still flaky. But electronic components like capacitors do break down over time, and load cells fail too. I've done a number of calibrations and replaced bad load cells in large industrial electronic scales, and always started by checking and cleaning connections with electrical contact cleaner, because unseen corrosion can cause large errors. Load cells are so sensitive to minute changes in resistance that you should never shorten the factory length of the shielded wires. But in a cheap digital powder scale, load cells and other components aren't worth servicing if out of warranty. I have also read that people solved drifting due to static electricity by wiping down the scale with an anti-static dryer sheet, but I've never had cause to try it.
I have a set of calibration weights to periodically check my scales, but only because the weights were in a box of reloading supplies I bought at a gun show. For many years, I simply did the same as my Dad, and kept a few jacketed rifle bullets of different weights to check my scales over a range of weights. I even took that a step further, and verified the exact weight of my scale calibrating bullets by taking them to my college organic chemistry lab, and weighing them on an incredibly precise and sensitive Mettler H-15 Analytical Balance. That scale was so sensitive that you could clean and weigh an object like a bullet, and then weigh it again after touching it with your fingers. It would then show a very tiny increase in weight due to any trace of skin oils deposited from your fingers.
