Digital thermometer for $7 from dr foster & smith... spiffy and accurate...
Backup of stick on the outside temp strip near the top, since it is just reading the glass temp it doesn't matter where it is.
I got a 250watt stealth heater from there for $17.95, it actually adjusts the temp to what the temp on the knob says.
I had a faulty heater once, had just setup the tank and was stabilizing things before adding fish. BUT, had a large pleco in a 1 gallon jar because his previous tank cracked and I felt bad so I put him in once the temp was ok... went to work... came home to floating and boiled pleco... heater set to 75, water temp 95... I could see water inside the heater... so I returned it... poor pleco paid for my mistake.
46 gallon bowfront, Dalmatian Mollies, Swordtails, Otos
75 gallon Lake Malawi African Cichlids
3 gallon nano desktop with Betta at the office