Garmin Panoptix P21-TR vs P21-TM

Ok, I am sold in squandering $1K on a Garmin Panoptix plus a Multi Function Display after a lot of research.

I see the difference between P21-TR vs, P21-TM as follows:
​(1). trolling motor mount vs. Transom mount
​(2). Power cable and Ethernet cable (13 feet vs. 30 feet)
​(3). Beam width (45 degrees by 90 degrees vs. 20 degrees by 90 degrees)

​(1) and (2) are obvious, but (3)??? can anyone help explain this please?

Q1: What are the 2 degrees?
Q2: Is 45 a wider angle cone than the 20? so 45 can cover more water than the 20?

I do mostly shallow water fishing under 60 feet, so I am thinking P21-TR will work better than P21-TM if TR covers more water (wider).

Example: 45° wide is 22.5° left and right from the center Main Axis of the beam ...

Example: 20° wide is 10° left and right from the center Main Axis of the beam ...

Example: 90° vertical is 45° above and below the center Main Axis of the beam ...

How one "aims" the Main Axis (by the housing position in the notched mounting bracket) will determine what the PS21 "Sees" in the water column ...

Rickie

Before you buy contact Brian at BBGmarine. He will have the best price.