Thermocline is a temperature change at a certain depth in the water. In some conditions the sonar waves will actually reflect or bounce off this temperature change and therefore it will be displayed on the LCR as shown above. To see the thermocline, you will need to go to the manual mode and increase the sensitivity setting.
One of the best ways to learn to use your LCR is to go over familiar locations. If you know what's under the water and can see it displayed on the LCR, then you're on your way toward gaining the experience you need.
