Ok here is the code.

<FORM>

F:<INPUT type="text" name="F" value="32"
onChange="C.value = 100/(212-32) * (this.value - 32 )"></td>

C:<INPUT type="text" name="C" value="0"
onChange="F.value = (212-32)/100 * this.value + 32 "></td>

<td colspan="2"><INPUT type="button" value="Click for Answer"></td>

</form>

And here it is in action.

wefuze.com/tools/temp-converter

Now if you understand java and stuff youll see how this works.

Now how can I adjust this code for other uses such as determining how many feet there are in how many yards?!