You could pass the data into the URL using links, and then capture the choice in the $_GET array. Obviously thispage.php needs to be changed, and some html could be changed if you literally want buttons. But here's the idea:
echo '
<a href="thispage.php?series=1">SERIES 1</a>
<a href="thispage.php?series=2">SERIES 2</a>
<a href="thispage.php?series=3">SERIES 3</a>
';
if (isset($_GET['series'])) {
$series = $_GET['series'];
} else {//if there is no choice, display series 1
$series = 1;
}
switch($series) {
case 1:
//display series 1
//e.g. echo...
break;
case 2:
//display series 1
break;
case 3:
//display series 1
break;
default:
break;
}