@snowonmyhead  wrote "...If indeed a barometer is hazardous."

I can't recall much about my old barometer (see below) but you can, as I've just done, both google and also asked a search-AI: "why is mercury in an old barometer potentially hazardous? - is it now covered by law?" Answers are Yes and Yes, with details given as to why mercury in barometers is potentially very hazardous, and the legislation/regulations that deal with it.

see also and first: @1956glyn message #2 and @therenewalworkshopltd message #3.

Depends of course what kind of barometer. A decade ago I inherited a barometer my grandfather, a hobbyist collector of nice old things plus antiques, had acquired c.1910, so obviously mercury/potentially hazardous. You can consult experts to get an item's valuation, age, maker, market interest e.g. auction house, museum curator/university departments with horology/science-instrument collections, pro horologists/restorers (condition, mechanism type, conservation advice), accredited valuers e.g. Society of Fine Art Auctioneers, Royal Institution of Chartered Surveyors.

A sister (who was looking after it) started enquiries with the local museum in the town where my deceased relative had lived and was referred on to one or two of the above experts. She was advised not to hang it so someone could see it through a window from outside, nor where visiting strangers would see it. She was also warned that no ordinary courier would handle it / be allowed to handle it. She was given advice on how to transport it if doing DIY delivery (I don't think the 2026 legislative/regulatory update would now hardly allow DIY delivery). My sister had her hubby drive it and themselves 300 miles to its new home, with the well-packaged barometer kept upright between her knees throughout.

Summary: get an old barometer checked by an expert and be prepared for legal regulations, and that no ordinary courier would transport it or isn't allowed to.