Numbers on a thermometer must strictly increase as they move away from the bulb.
The 4-cell boxes in YELLOW are mystery squares. Each mystery square is comprised of only 2 digits. (such as 8-5-8-5)
The mystery square to the bottom left sums to half the total of the one to the top right.
F-puzzles link - link to solve online
Lösungscode: Row 6 followed by Column 8