PING))) data bouncing all over

I have copied the demo code and uploaded it to an Arduino Mega. It is directed down a hallways approx 20 feet in length. The output is bouncing up and down outputting serial data like what is below. There is nothing moving in front of the sensor. Any ideas what is going on? Thanks. This is fun stuff!

41in, 105cm
101in, 258cm
40in, 102cm
40in, 104cm
43in, 109cm
40in, 104cm
145in, 371cm
41in, 105cm
41in, 105cm
41in, 105cm
99in, 254cm
40in, 102cm
100in, 255cm
102in, 260cm
145in, 371cm
99in, 253cm

Testing distance with a solid flat object, it seems to only be able to accurately measure up to 50 inches, which falls pretty short of the 3 meters it's rated up to.

What you're talking about may be plain to you, but to us poor people who are just reading this, it gives precious little insight into what you're doing.

You're using some form of distance sensor connected to an Arduino Mega, using some form of demo code, and its not giving expected readings........

A link to the hardware and the code would be a huge help.

It is directed down a hallways approx 20 feet in length

You could be getting reflections off all kinds of things - these things don't have a very narrow beam, or you could be getting delayed reflections from the previous pulse. You may get more consistent readings if you slow the rate of readings down, but without more details of the setup, dimensions and your code, it is difficult to say.