Hi Mat
Thank you for your detailed and very helpful advice to solve my problem. I am delighted to say your suggestions worked and have now been implemented on our live site see https://database.crickladecourtleet.org.uk/river-levels/
I did have a problem reformatting the dates using the gutenberg editor, the date defaults back to its original format and any reformating is ignored. The classic editor works as expected. Also there is no way to reformat dates on a bar chart. That said it all works fine now and I am very happy with the result.
Visualizer is the best plugin I have found for our needs, no doubt other premium plugins could do the job but as a small charity we cannot justify additional payments if we can find a way without. Visualiser did work correctly over last winter but I think an update must have caused it to stop working on our site. My next step would have been to find a way using the Google Charts API directly so you have saved me a lot of time, as well as restoring my confidence in Visualiser.
Thanks again for your help.
Best wishes
John
