"You regularly refer to the long dated govt bond yields in your commentary with the comment that 4% yield is ok for stock markets but if yields get to 5% this could be a headwind.

"What chart is best to monitor this aspect of investing?"

David Fuller's view The key rate, so often illustrated and mentioned in this context, is US 10-Year Treasuries (historic, 10-year weekly & 5-year weekly).

What I have discussed regarding headwind yields is a personal hypothesis. Other factors will also influence sentiment. Yields will be higher in many countries before they negatively affect equities. What I would be reasonably certain of, is that US 10-Year Treasuries at 5% to 5.5% would pose a greater risk for stock markets than the current yield. Meanwhile we watch the charts for 10-year yields and equity indices.