What are some possible source of errors in a science assignment?please list all the possible errors!!!!

Just to list a few that are
generic:

Equipment - Either wrong equipment used or the
equipment does not measure to the proper level of precision. If you used a beaker to
measure 30 mL instead of a graduated cylinder you could only measure to .0 mL where as
with a graduated cylinder you could measure to the
.00mL

Contamination of chemicals if it is
chemistry.

did not conduct the proper number of trials
normally 3 is acceptable

Rounding of data to
early

Humidity exposure of items such as salt that obsorb
water vapor from the atmosphere.

It would help to know the
experiment but I hope these help.