Why are there discrepancies in my circuit evaluation?

[master_mind]

i am doing an evaluation on a circuit in which i measured all the values e.g the current, voltage etc, and i also calculated the values.
there is a large diffrence in between the measured and calculated values, can anybody give me some reasons for this.
ive got some which are - diffrent resinstance in the wire, personal errors, reading the dial's wrong, the tolerances on the components.
is there anything else which i could talk about?
thanks

 

[ehild]

Yes, the internal resistance of the meters can be serious source of errors. Show your set up, please.

ehild

 

[master_mind]

thanks for the help,, also i am new on here an I am not too sure how to put my circuits up,, but anyway I've handed my work in!