which would be the true reading when idlein the greedy boost gauge reads around 500 and the hks boost controler reads 400 so when the controler is set at 1.4 bar and the car boosts to this i am getting 1.5 bar on the gauge and the warning light comes on which would be more accurat?? cheers

 

Do they both read 0 or 1 bar abs when engine is Off?
if you have analog boost gauge then probably the gauge.
They can be very inaccurate