So somebody was showing me how strong their magnet was but I was sure my'n was stronger....time for a magnet sensor!
We found a nice cheap Hall effect IC, I settled on the A1302KUA-T from allegro microsystems. First thing to do was delve into the datasheet, most of the characteristics were at 1mA output and 0-5V(ish) output from a 5V rail, so a simple divide by two attenuator totalling approx 5K would do the job to give our 0-2.5V range on the DrDAQ. Given that the pull up on the DrDAQ to 2.5V is 100K there wasn't much point for another buffer since the output will be within a few percent of the expected value.
So I drew up the schematic, see below, and whipped up a PCB. The Eagle eyed among you will see that I confused ground and Vout (see page 3 on the datasheet) so I had to cut the PCB and extend the legs on the IC (I knew I should've just done this on stripboard)
I plugged it into the DrDAQ and took the zero magnetic reading, point2 in the DDS file and from the datasheet set 200G for 0.13V either side (1.3mV/G and we've devided by two).
Finished....so I started up picoscope and held up the 'strong' magnet to my Hall sensor (and then backwards as well) and then I held up my magnet to the sensor (and again backwards)....My magnet went completely out of range
So I know it's not a completely fair test but I think I won, Enjoy.