WebPlotDigitizer! It’s a great tool.

Here is my attempt at digitizing that plot and then log-scaling the vertical axis.

I of course wish it was fully open source

Allow me to introduce you to Codium

I too was similarly confused by the original comment at first, but I think they’re referring to the fact that 6pm GMT is 7pm in London during the summer (BST), and 6pm in London the rest of the year. It seems OP and “them” are both correct in that hypothetical exchange.

That’s what the meme is saying too