Ultrasonic Sensor

I have a Parallax PING))) Ultrasonic Sensor Range Finder Module. What I wanna know is the beam width at its max range? And is there an algorithm to measure it ?

The algorithm is called "trigonometry"

AWOL:
The algorithm is called "trigonometry"

.... but it needs the beam angle to start with.

I didn't see the angle in their info here, it just says it's "narrow".

What I wanna know is the beam width at its max range?

Then you will have to measure it.

is there an algorithm to measure it

The algorithm is "to measure it".
Maybe you are using the word algorithm incorrectly?

Note that this is not a problem that produces a simple answer, as the beam fans out at maximum range then the type or nature of the reflecting surface becomes more critical for detection.