Someone wrote:
>
>Along the same lines: How do you mark down the original calibration on JW
>508s and 509s ? I use a steel needle to scratch it into the brazed window
>bezel but sometimes more scratches are added during handling and then it's
>gone. Is there a marker pen that uses non-transparent non-removable ink
>and has a fine tip ?
>
Staedtler Lumocolor 313 Permanent (available at any drafting supply
store).  Get the size "S".  Not only is it waterproof, but it's
wasserfest and indelebile.  :-)

I use it to mark UV '74As that I've code-protected and later erased (but
that's another thread).

--Matt