What exactly does a manometry test?

I got my manometry results a couple weeks ago. I was shocked to find our that the results came back normal, but what dies that mean? Obviously something is not functioning properly since I get heartburn at all hours of the day. Does a manometry only test the strength of the LES during swallowing or can it evaluate the functionality of the LES between swallows?

Basically, if a manometry test comes back normal, does that just mean my swallowing is functional or does it mean something about the overall strength of the LES?

Thanks for the answer Bill. I am not trying to figure out whether or not I have GERD since I have been diagnosed for several years now. I am just trying to get an understanding of exactly what is responsible for my heartburn. I had been convinced that it had to be caused by a weak LES and that was why I was surprised to be told my manometry results were normal. My other tests have shown that I have a small hiatal hernia. Could that be responsible for all of my heartburn, or what else could be going wrong?