If I understand you correctly, a mechanical gauge should have a small
oil tube going to the back of the gauge directly from the
oil port on the lower left front of the block, so you should be seeing a true reading of fluid pressure. Typically about 10 lbs higher at cold startup, and after everything warms up you'll see maybe a 10psi drop. Standard SB
oil pumps are typically 35-40 psi. A high volume pump can see 60 psi, cold.
If this is not the case, and there is a sending unit with a wire, then it is an electric gauge, and the readings don't surprise me. It is basically an idiot light that goes to a gauge instead of a light.