you have to experiment with it a little, i always try about mid ways first then just keep changing it if its not working. thermocline is a section of the water at a certain depth, that when the water gets very warm, attracts the most fish because, its cooler and can have more oxygen at times, this can be a challenging part of cacthing fish at times in the summer, you need to try to get some baits in the thermocline. if not now diffently when the water gets alot hotter.