Dual rev/speedo counter needles below 0
After replacing my old single rev with a dual cluster all was working fine, then after removing the battery to perform other work, the rev and speedo needles have dropped below 0, but move normally (but 1000rpm and 10mph less).
I've opened the cluster and moved them manually to 0, and it works, but after turning off the car for around 30min and then putting the key in the ignition it seems to drop them back down to below 0 again.
Any ideas how I can re-zero it successfully?
Note: The main central speedo remains at 0mph like it should.