<Script>
function comparision(){
val = document.compar;
if(val.model_id1.value == "" ){
        alert("Select a model");
        return false;
}
if(val.model_id2.value == ""){
        alert("Select a model");
        return false;
}
if(val.model_id1.value == val.model_id2.value){
        alert("Choose 2 different models to compare");
        return false;
}
return true;
}
</script>
