https://www.youtube.com/watch?v=RODdSqKzwCUMartin looks at the collection of thermometers and temperature probes he has in the lab, and looks at the difficulty of measuring temperature both accurately and reliably. Using assorted multimeters with temperature measuring ability and assorted IR measuring ranging from cheap to quite expensive. He explores the limitations of each one, and especially the field of view of each, and how that translates in practise to what is displayed as a temperature.
He uses the closest he has to an isothermal chamber, using a temperature controlled chamber to emulate a black body radiator, using contact measuring to do sanity checking on the chamber sensors.
You can see the various offsets, along with the differences between each method in both accuracy, stability and how attachment and aim has an influence.
Tip for next time is get some thick copper plate that fits in the bottom of the chamber and blacken it using a candle, which will give a surface that has an emissivity of 0.99. Ideal black body radiators are a pure copper ( or better silver) block with a surface consisting of sintered Platinum black fused to the surface, which makes a good black body from cryogenic temperatures to the melting point of copper. Use pure Pt and it works up to the melting point of Pt as well.
Ideally you want a chamber that is black inside ( Pt black, soot or thin matt black spray paint) with well insulated walls and heating evenly inside, with only a small hole for radiation to escape used as the view port.
As well there is a definite need for a calibrated thermometer for checking, or a triple point cell to get a good -0.1c reference. A heated stirrer plate and a beaker with water containing Indian ink ( basically powdered carbon in suspension) will help in both checking at higher temperature, up to 90C in this case, as Martin lives now at altitude, where water boils at under 100C.
