Unfortunately, Hydrognomon is unsupported. Read the first question in the FAQ for more details.

There is a a page and a community group in Facebook. You could try joining the group and posting any questions there, though it’s not certain you will receive a response.

You can contact (some of) the developers and maintainers by emailing openmeteo@itia.ntua.gr, but, again, you won’t necessarily receive an answer.

Hydrognomon has been developed by the Itia research team of the National Technical University of Athens, Greece.