Thanks Ray. As so often, the mere fact of posting and getting a response gets you thinking! My device was set to static IP and could be accessed on the local network, but not remotely. I tried setting it using DHCP, and then the Zimmerman calculation was working! Looks like it may be an issue with my router. Almost looks like an IP clash – but I’m using the same IP as my previous OpenSprkler (which is off the network). Anyway, I have reset it now as a fixed host on my router and DHCP on teh OpenSprinkler and everything is working fine. Thanks again.