[Aetae]

В современных браузерах можно на чистом css:

<style>
form > span {
    display: none;
}
#R1:checked ~ .R1, #R2:checked ~ .R2 {
    display: inline;
}
</style>
<form id="calculator">
    <input type="radio" name="type" id="R1" value="R1" checked/><label for="R1"> R1</label>
    <input type="radio" name="type" id="R2" value="R2" /><label for="R2"> R2</label>
    <br />
    Вы выбрали тип: <span class="R2">R2</span><span class="R1">R1</span>
</form>