Cheap way to track interior temperature

Now that I got my windows tinted, and after reading up about how much light and heat they block out, I got curious about the interior temperature of my car. I could spring for a fancy thermometer but I was in Cargo Largo the other day and saw a Taylor dial food thermometer for $2 (Taylor makes good food equipment) so I bought it and tucked in above the visor on the passenger side. I was surprised to see that it read 135 degrees friday when I went to work (but it was sunny, I had left the sunroof sunshade open, and the car was facing the east).

But for $2 I know now the temp inside, not a bad way to spend a couple of bucks.