Experiment - The Effect Of Number Of Turns On Stength Of Magnetism

Hi,
I have a Physics ISA tomorrow based on the experiment where you wrap coils of wire around a nail and then find out if increasing the turns around the iron nail increases the strength of the field by seeing how many paperclips you can pick up. Pretty basic and i'm sure you've all done it!

Just wondered if someone could talk me through all the details, such as errors that may have occured etc.

I have this already (although it may be wrong);

Variables

Independent – number of turns (coils) Discrete?
Dependant – mass of paper clips lifted (grams) Continuous
Controls – length of wire
current (in amps, shown on the ammeter)
p.d (in volts, from the power pack)
nail used (length, width, mass, already magnetised etc)

Increasing...

Precision - instead of picking up paper clips, use smaller pieces of metal
Accuracy - use fair, precise equipment and keep control variables the same
Reliablilty - repeat results and obtain a mean or repetition by other people obtaining the same results

Would appreciate help ever so much!
Thanks in advance.