The temperature scale and the color palette for the active infrared image (or all infrared images in the viewed folder, depending on the Same Palette/Same Range settings) is shown at the right-hand side of the main window. The temperature scale window shows the temperature range selected for displaying it against the palette – it gives the correspondence between temperatures and the palette of colors used to represent them.
If you do not need the temperature scale window at the moment, you can temporary hide it by clicking on the sigh 
in its top right-hand corner.
For further information see the following topics:
§Selecting temperature span and palette
§Same Range and Same Palette options