No debate here crappiepappy, I’m just hoping it is a chance for us to learn – and I don’t rule myself out from the learning part here. I don’t think that the comparison of your car and thumb to sonar is accurate. Your brain uses the visual reference of what your eyes see and interprets size from that mainly based on past experiences. Sonar measures only distance and can show signal strength. Your thumb would show up on sonar closer and possibly as a stronger sonar signal which is expressed in colors or shading but not size or distance. The screen snapshot that Kosmo posted was with the Upper Range menu set to 7 feet deep and the Lower Range menu set to 30 feet deep. This is not a zoom function so the distances shown by the sonar should be accurate.

My calculations using a more accurate ruler and zooming in on the image this time:
- Overall height of the image = 8 inches.
- Vertical distance displayed in the image: 23 feet [30 feet – 7 = 23] or 276 inches.
- Each physical inch of the image represents 2.875 feet [23 (feet) /8 (inches)] of water distance or 34.5 inches [2.875 x 12].
- 1/10th of an inch represents 3.45 inches of water distance [34.5/10].
- The fish measured 2/10 to 3/10 of an inch in height.
- So the fish was somewhere between 6.9 to 10.35 inches in height [2 x 3.45, 3 x 3.45].

Now, since I was not working from the original image and I was using a ruler to measure things with I could be off a bit due to blurring the image by zooming in on it, but I believe that my calculations are in order. If not, please tell me where I messed up.