Apologies to all those who realised this long ago, but it has taken me several nights to debug a multi choice if then chain.
My problem arose from a misinterpretation of how the Maths Thing uses the Between condition.
My initial interpretation was that the upper and lower boundary values were inclusive ie pairs of integer values could be separated by the conditions:
Value between 1 & 2
Value between 3 & 4
Value between 5 & 6
Through experimentation though I have discovered that they are exclusive so the proper tests are actually:
Value between 0 & 3
Value between 2 & 5
Value between 4 & 7
Once again apologies to those who were already aware of this, but hopefully this post will clarify the issue for other newbies like me.