2-Mounting Portable or Fixed-mount - Portable units are entirely self-contained and usually include a carrying case and suction cup transducer hardware. Example: fish finder featuresEagle Fishmark 320 If fixed-mount you will usually attach the transducer to the to the transom of your boat. If you have a single hulled fiberglass boat, you can usually mount it to the inside bottom of your boat. This is known as shooting through the hull mounting.

3-Dual or Single Frequency Transponder Dual frequency - has both 50KHZ and 200KHZ sonar and is used for very deep water or salt water. It will penetrate better in the dense salt water and give a better signal in water over 200 feet deep. Single frequency - uses only the 200KHZ; used in inland lakes and fresh water and under 200 feet depth. Example: fish finder featuresLowrance X67C Target definition is actually better with the higher frequency but if you plan to do both fresh and salt water fishing & both shallow and deeper fishing you're better off to get the dual frequency.

4-Temperature gauge Water temperature greatly affects the behavior of fish. Fish are cold blooded and assume the temperature of the water around them. In lakes, there are warm layers of water and cooler layers. Where these layers meet are called thermoclines. Many times bait fish prefer the areas above the thermoclines while the larger game fish prefer in or just below it. This difference in thermoclines can be seen on the fish finder display screen. The greater the temperature difference, the denser the thermocline shows on the screen. Example: fish finder featuresNavman F4500