It's a nice meter.
On the 500mV range, the accuracy is +/-0.1% + 5 digits, that will be +/-550uV (when using REL Q mode)
So if the meter reads 1mV, then the actual value could be anywhere between 450uV and 1550uV
If you are measuring current with a 10Ω resistor then it's somewhere between 45.0uA and 155.0uA