Some possible sources of errors in the lab includes instrumental or observational errors. Environmental errors can also occur inside the lab.
Instrumental errors can occur when the tools are not functioning exactly as they should be. An example of this error is a thermometer used to measure temperature. If the thermometer is not calibrated correctly, it can cause an error. An observational error example would be if the experimenter did not read the thermometer correctly when recording results. An example of an environmental error is when an air conditioner in a room causes the table to vibrate slightly and this vibration causes the measurement to be slightly off.