2391 is normally seen as a difficult qualification in the elecs industry, which is why it seems to be used in job ads, assuming if you have 2391 you must be good etc.
Its suggested that you have 2 years + experience in the industry before starting to study for 2391, all pointing towards saying how difficult it is.
Its a 2 part test qualification, you need to pass a practical test, where you have to do an inspection of a standard test rig, where an examiner will watch your every move and fail you for missing a test, doing it wrong, forgetting to null the test leads etc. They also check your results again what they should be, you have to be pretty close to what the official result is etc.
The 2nd part is a closed book exam which is not graded, its pass or fail with no results or reasons given, just told you pass or fail.
The real story is......most sparks aren't academic and not great at exams, so this is why it gets a 'difficult' reputation, if your the more academic type you will walk the exam no problems but without experience you will really struggle with the practical and most likely fail.
You need to get some hours logged with a tester practicing the different tests, how to configure the test leads for each test, how to conduct the test correctly, for example r1r2 on a ring, figure of 8 connection of the conductors etc.
If you don't have your own tester you really want to learn on the same tester that you will use in the exam, you really don't want to be shown an unfamiliar tester on the day etc if you need to borrow one from the testing centre.
best advice if you want to go ahead:
watch the spark you work with more closely & ask questions
take 17th edition exam first, as this knowledge will help with the 2391
practice a lot with the tester
then book the 2391 course
good luck
Ps. 17th is open book, best advice for this is the read the book through a few times and speak to a spark or trainer to clear up any points you don't understand, once you are familiar with the book you can understand what the question is asking and find the correct charts/graphs in the regs book to answer questions
Although the exam is open book you do not have time to look up each question you need to know the book pretty well and be able to answer 95%+ of the questions without looking, then double check anything with your spare time at the end
Books to get:
Latest on site guide
Latest 2391 inspect and test book
Latest regs book
Possible Latest PAT testing book might help
Books aren't cheap probably looking at £100 all in afaik
