Sounds like it. But you can also put some element with a certain width kind of as ruler into the page to see how the stylesheet changes with which size. For example put a div with a width a height of 10px and some background color so you actually see it, and then set a width on it in different media query rules, like:
Code:
@media only screen and (min-width : 860px) {
#example {width: 860px;}
}
@media only screen and (min-width : 1280px) {
#example {width: 1280px;}
}
You will then probably see it changing when the specific minimum width is reached.