HP-35 for sale - but which version do I have?

[chancewest]

I have a very old HP-35 that used to belong to my Grandfather for sale. How do I go about working out which version of the HP-35 I have?

Clues, based on some random scanning of webpages:
* Small square keys with text printed above.
* No "red dot" on power slider.
* Power supply plug is circular and has two pins - that's why I haven't been able to turn it on and test yet.
* Serial number begins "1302S", followed by five digits.
* No dot on five key.
* Comes in a large grey plastic carry case.

If you have any questions ask away!