Tried out the new frequency option in latest Picoscope release (6.4.95.0). The two attached images show capture from airflow meter in 2005 BMW 320D
The first image is voltage setting and not much use as the voltage stays at 5volts no matter what the air flow. The MAF just increases the frequency of the signal as the airflow increases.
However the second image is using the frequency set 1khz-20khz.
This gives a good capture of airflow signal from idle to full open throttle and back.

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That's a real nice clean frequency trace Paddy. The last time I used the "frequency" feature, it was so noisy that it was hard to read.

You possibly had the sample rate too high. High sample rate not required. I think I had that down to 50ks to reduce noise

Nice, Paddy.  You can even see the individual cylinder gulps in that capture.   ;)