eheim jager 50 watt heater

[flipzed]

i have a question for somone who has used one of these. i just picked it up and trying to set it up and it says u adjust the blue temp dial to desired temp. well theres no mark on the heater for where u want to set it to. then once thats done u move the red calibration dial to fine tune it, but am i missng somthing how do you know where to set it in the first place..

thanks for any help