boost gauge readings.. help..

[D Turbo Lyle]

thanks for helping guys. Ok so its a mechanical boost gauge it isnt brand new prob a few yrs old sitting in my pals shed! It seems to be sitting at -8 below 0psi when its unplugged and even if its idleing its sitting at -7,-6 ish psi. as soon as its almost getin onto the turbo it whips up 0psi and if i put some foot down am getting 11psi when on full boost. Maybe i should just get myself and new mechanical boost gauge or a digital one. Nothing to worry about but the boost gauge then...?? cheers for any help greatly appretiated