Assuming it's calibrated the same as the US model, you can figure that the center is 40 PSI, the extremes 0 and 80, and interpolate from there. I'd be pretty surprised if there's any difference in the mechanics of the gauge or the sender. It's more likely they just changed the markings. If that's the case, then you should typically see the needle a few degrees above the center position when running normally, and somewhere in the vicinity of the 1/4 position at hot idle, representing something in the neighborhood of 45 PSI running and 20 at idle. If that's the case, you won't gain anything but markings by changing it.
The gauges mount simply to the back side of the cluster, so if you really must have markings, you can just take the gauge out and paint whatever you want on the face. If you opt for a US type gauge, be a little careful, because there were some changes in the cluster over the years, and even whole clusters that are interchangeable may not have interchangeable components.
