On Monday, 30 October 2017 18:51:58 UTC, Desperate Dan wrote:
When mig thermometers were used the regulation height was 2.5cm to 5cm above ground with the thermometer bulb “just touching the tips of the grass”. (Are mig thermometers still used?)

mig have been taken out of use at all MetO sites for H&S reasons, however grass min thermometers are alcohol in glass and are still used at manual MetO sites such as Copley.
We have artificial and natural grass here. The artificial normally reads higher.
Ken
Copley
Teesdale