I have some rather specific questions about how to teach real number representation at A Level. I hope some of you more experienced teachers can help. It seems to me that the progression in terms of difficulty is: binary fractions to denary and vice-versa; floating point positive numbers; floating point negative numbers; normalisation positive; normalisation negative. I am intending to teach the topic this year over at least 4 lessons and come back to it several times during the year. My questions are: do you agree with the above progression? Is 4 lessons enough initially? What do I do about differentiation? In my (limited) experience some students are never going to be cope with all of it, so how do I differentiate for them? And just to preempt certain posters, any replies to the effect that people without a CS degree should not be teaching the subject are not helpful!