Accuracy expectations: is -8 s/d acceptable on an entry-level automatic? · RWI-31187

Start with how you measured it. Comparing against a phone clock once a day for a week, at the same time, and noting the offset is reliable enough. One 24-hour reading isn't, because rate depends on wrist time, position overnight and state of wind. Average across several days before deciding anything.

Compare the observed rate with the exact caliber and cased-watch specification, if available. An example such as -8 seconds per day cannot be declared acceptable solely from its price category.