Can this keep my res at 68 degrees?

Quick question about this aquarium heater... it's the penn-plax cascade heat. It shows a temp from 68-89 degrees but when I put it in my tank and try to put it at 68 degrees it shuts off. Can anyone tell me anything about it? How to use it? The instructions don't really help at all. A pic of the product is attached

It s a heater so when you put it at 68 and shuts off means the temp is abouve 68 degress

Lol...awesome

And you couldn't figure that one out yourself.........common sense is all that's needed .........Lol...I'm assuming that you've tried it at different temps to make sure it's WORkING ......yes???