Thanks again!
I am a MSc and not uninterested in math, so I thought this would be easy to understand - I was disappointed, however. But of course, I graduated many years ago.
So, I still have a number of questions, if you care to teach me:

I managed to get the binary bits from IRScope, manually break them into bytes of 8 bits and reverse them. But
- Why reverse?
With help of the Windows Calculator I computed the hex values. 100-B5=4B= 100 1011 is also ok, but
- Where does 0x100 come from?
Reversed 11010010
- Why insert 010? Where does it come from?

Isn't there an easier way to create the checksum?
Or is it a secret of Fujitsu, which you have revealed?