What is this diode symbol?

[sharks]

1. The problem statement, all variables and given/known data
I have looked in all my textbooks but i can't find anything about this diode or what it does?
Here is the symbol of that diode (from a City & Guilds past exam paper):
http://img5.immage.de/2204diode.jpg

2. Relevant equations
It's just an unknown diode symbol to me, and there are no equations that i know of associated with it.


3. The attempt at a solution
At first look, it appears to be a Zener diode, but it might not be, unless it's an old version of the Zener diode??

[Mardoxx]

zener diode with (threshold??) voltage of 2V
i.e. anything over 2v is aloud to pass back through

[berkeman]

1. The problem statement, all variables and given/known data
I have looked in all my textbooks but i can't find anything about this diode or what it does?
Here is the symbol of that diode (from a City & Guilds past exam paper):
http://img5.immage.de/2204diode.jpg

2. Relevant equations
It's just an unknown diode symbol to me, and there are no equations that i know of associated with it.


3. The attempt at a solution
At first look, it appears to be a Zener diode, but it might not be, unless it's an old version of the Zener diode??

As Mardoxx says, it looks to be a variation of a Zener diode symbol:

http://www.google.com/images?hl=en&gbv=2&tbs=isch%3A1&sa=1&q=zener+diode+symbol&aq=0&aqi=g1&aql=&oq=zener+diode+sym&gs_rfai=&start=0

It's not commonly used, though, at least not in the US. Here, a Zener symbol generally has angled tips to the cathode line, with an angled tip on both sides. A Schottky diode generally has two right-angle tips to the Cathode line. So having a single right-angle tip on the cathode line is unusual.

[sharks]

Thank you both of you. Your help is much appreciated. :)