How divide / multiply low frequency pulses to create a new frequency

The old school way is TTL.

Here are more.

There still remains some sections of the Stuart Highway (Northern Territory Australia) that has no speed limit.

How lucky (NOT) I am.
The very first production run of Subaru Foresters (mine) used the Legacy gearbox which uses a 2 pin analogue VSS.
So all the above was in Vain.
Now what to do? Replace the Hall effect sensor with an inductor + amplifier ...... and the other irritation ... calibration.
Any suggestions?

All done and now back in Darwin .... a mere 5225 km in a more sane time frame.... 10 days.
I found I could sample via the audio IN on a laptop (EeePC), easily convert and correct the signal and pass out via audio OUT.
I could not dedicate the lap top to this sole function so I bought the magic box from the States.
Made from a section of PVC water pipe, split length ways and held around the CVJ cover with hose clamps.
Two small pieces of pvc keep the halves aligned and the points of the screws attaching these protruded slightly so when clamped prevented the halves from sliding along the CVJ cover. Photo attached.
The magnets were bolted and epoxied to the PVC. I was worried the the PVC might soften and deform but at a sustained 160 kph across the desert it failed to fail.
Calibrating the Dakotadigital device was more like witchcraft than science but I got there in the end.
A few things I need to test ..........
Output from the magic box appears slightly non-linear.

Better than pulling out the gearbox. Faster and cheaper!
And I learnt new stuff which always beats taking the same old path.

Greg