I'm measuring an assortment of old electrolytic capacitors ('elcos') to see if they are still okay, using my digital multimeter (a simple Duro AL-205). I noticed that most of the values are higher than the rated capacitance but that's okay since I know tolerances are usually in the -20% to +50% range.
But when I have an elco rated at 320uF, (yes, 320 not 330) 6.4 Volt but it measures as 844uF, I'm sure something's broken. Is there some fault mode in elcos that can cause higher-than-rated values? I'm careful not to touch the terminals with my fingers when measuring, so any parallel resistance does not influence the result.