Physics Lab error analysis?

Hi! Guys. I did a lab in my Physics class. We used ammeter to set the current to a certain amps .One end of the ammeter was connected with a resistor and the other end of it was connected with power. When current was made accross the circuit, the voltage was read on a Multimeter and we were asked to find the resistance. What might be signifcant sources of error. I need atleast three of them . Thank you!