Average and max amperage figures seem to be 10A higher than expected on AC charging?

See screenshot below from recent AC charge (Tesla Destination Charger).  Voltage mean/max look spot on, however the amperage summary at the top doesn't seem to tally with the data below it.  The car sat on 10A the whole time, occasionally dipping to 9, so the mean was 9.91A (from the datapoints available) - however it is displaying mean 19.82 and max 20A?