[JayG]

Just checked the temperature in my greenhouse.

Max/min thermometer: 13C on the "min" scale, 10C on the "max" scale (they should be the same!)
Weather station remote electronic sensor: 17.8C ( )

Laboratory-type mercury thermometer; 13C

Thought this might be a useful potential warning for those relying on such devices for checking frost risks or setting their anti-frost heaters.

In my case it looks as if the minimum scale on the max/min thermometer is the one I need to use; will do another check when the temperatures are higher to see if the error is the same (with my luck the "max" scale will probably be more accurate at higher temperatures!) 

[rainie]

Hi JayG, only just seen this.

Have you read them all since this reading? I am wondering if it has happened again.

[8doubles]

A complete stab in the dark but if it was windy and the greenhouse took a buffeting might the min/max indicators have vibrated back down.

Min -4'F max 80'F in the greenhouse yesterday.Broad beans and onions looking good though.

[JayG]

I put all 3 devices right next to each other and left them for about 20 minutes to make sure they were all equilibriated. The max/min thermometer was read directly from the liquid scale rather than the metal indicator thingies! A max/min thermometer should read exactly the same at both "ends" when read like that.

Of the three only the lab thermometer is a proper scientific instrument so my guess is that the others are not to be trusted without using a "correction factor".

Working out what that is at both ends of the potential temperature scale might be a bit problematic, although I am personally more interested in the accuracy of the readings round about the zero mark!

[Kristen]

The "kids" are bigger now, but when they were little and apparently we needed a thermometer for the paddling pool I picked the "most optimistic" one in the shop

[waddecar]

My min max thermometer usually reads 1C lower on minimum side

[JayG]

My min max thermometer usually reads 1C lower on minimum side

That's pretty good (if they're both something like correct!) 

[8doubles]

Mine read the same on the C scale but are slightly out on the F.
Anyone know a thermometer recalibrator .