10:30 Filters changed and zero'd. Gas NO : 0/) refill needed. (last ordered 8/5)

Issues with zero'ing at Cradlewell - would not stabilise. This happened last service as well.

Attempted to zero manually NO by removing the solenoid T junction at the Sample port, and connecting the scrubber pipe directly onto the Sample port. Left for 20 mins but was not stabilising. Subsequent monitoring at AirMonitors site shows this is has been running with some negative lows (as if offset dipped) since 18th.

Further investigation needed.