Eheim Jager heater operation question

Before posting here I've read quite a few threads about this pain in the ass heater and haven't found any answers so I hope some people more familiar with it can help answer a few questions.
I have a Jager 300w in my 180 and my first question is how exactly do I calibrate it? I previously turned the heater off for 15 min and one time I put the red indicator on the current temp in the tank as soon as I turned it off and one time right when I turned it back on. Then I moved the blue moveable temp portion of the heater to what I wanted the temp to be at, 78.5. Each time I waited a few days to see where the temp ended up and it would drop to about 76.5 to around 78.9. Which brings me to my next question. The red indicator moves 4 clicks in each direction, does that mean plus of minus 4 degrees or something or what exactly does it do? And my next question, I want my tank at 78.5 really, but plus or minus a degree through out the day is fine as long as it is constant so if someone could just tell me how to accomplish that it would solve my problem and I would be very grateful.
Thanks

 

I have the 250w and the directions say to switch heater off and un plug, measure water temp. With accurate thermometer. Turn indicator arrow (red) to point to the measured temp. Set desired temp. With the temp selector ring (blue)

 

What kind of thermometer are you using? And how old is the heater?

 

The heater is a few months old and I have 2 digital theostats. I lost the instructions. So do you set the red before or after plugging it back in? And then turn the blue to the desired temp right after?

 

Set the red first then the blue then plug it in.