I wonder if it's a 'symmetry' kind of thing? Although mine is a lot older - when under normal running, the oil pressure needle is pretty central, the ammeter needle is central and the water temp needle is central.

If standard running oil pressure for yours in 2-4 bar, again, the needle would be 'central -ish' at just over 3 bar.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10