Faulty TVR Oil Pressure Gauge??

[DIB]

Hi, Wonder if anyone can solve a query for me. The oil pressure gauge on my '84 TVR 350i sweeps right across to maximum when the ignition is turned to the on position. Once the engine has been started it returns to a normal reading. Does anybody know if this is a fault or if it supposed to do this? I am worried about screwing the gauge up.........

Thanks in advance.