All above advice on GN3 is spot on,but i have to add a small addition,it would be not to just read and memorise the details,but ensure you understand the principles that are being applied to the tests. It is surprising how many lads who know the methods and requirements backwards,but cannot explain the fundamental reasons why these are applied.A quick example is a conversation i had with an experienced spark a while back,discussing the "pessimistically low IR" on a large installation,now this,as we know,occurs even with new installs,with all those extra parallel paths...but he was insistent that it was because the larger installations MUST have increased likelyhood of problems due to size. He would not accept that even a run of brand new cable,when of sufficient length,would fail the standard IR test. So,get the fundamental bits fixed in your mind,and all the rest is built on that.Only my twopenneth'...