A Newby Question ref Thermometers

[paulfg]

I have single wall stainless steel flue pipe and have ordered a Stovax magnetic flue thermometer
(broken link removed to https://www.ebay.co.uk/itm/253612292424)
I know it wont stick with the magnet but the listing says to use either the wire or screw provided to fix it.
My question is what difference in flue temperature does stainless steel give compared to black steel type ie plus/minus .Do in need to add/ subtract from the showing temp .
If I was to buy a probe type thermometer what is suggested as I have read that they are made for twin wall pipe
thanks

 

[begreen]

Surface flue temps are only approximate. You will not need to do an adjustment unless the thermometer is placed under 15" from the stovetop. At 18" the surface temperature reading will be approximately 50 to 75% of the internal flue gas temperature.