What do the numbers mean on the OP gage?
 

on most cars the Oil pressure gage reads in PSI with some accuracy, on MBs you get Zero to Three. Mine pegs at three when rolling down the road and hovers around two when warmed up at idle. is there any value assigned to the numbers or is just a little better than an idiot light? is it roughly kPa?

It reads in BAR. 2 at idling and 3 when off idle is perfect. 1 BAR is equal to 14.5 PSI

Some light reading if you're curious:
http://en.wikipedia.org/wiki/Bar_%28unit%29

makes sense 1 BAR = 100 kPa = 14.5 PSI

Gotta love the metric system, it's all related to real world stuff, not arbitrary like the US system

1 kg = cube of water 100 mm by 100 mm by 100 mm = 1 liter

0 C = water freezes 100 C = water boils at sea level

1 bar = normal atmospheric pressure at sea level

The gauge us not terribly accurate, unfortunately, and tops out at 3 bar or ~45 psi while the oil pressure typically exceeds 3 bar when the engine is above ~1000 RPM. The factory notes that apparently low oil pressure at hot idle is not a sign of trouble so long as the pressure rises as soon as the engine is above idle.

I have a separate mechanical oil pressure gauge on my '95 E300D; it registers over 60 PSI (~4 bar) when the engine is cold and first started. Hot idle is between 15 and 20 psi or just over 1 bar. The factory gauge shows closer to 2 bar at hot idle so there's a significant error.

Jeremy

This is ona OM617.952
The actual Oil Pressure on My Car can go up to 97 psi; about 6.69 bar.

The Pressure Relief Valve in the Oil Pump opens and 110 psi; about 7.58 bar. So that would be the most pressure you could get out of the Oil Pump.

At a Hot Idle I get 1.5 bar; about 21.75 psi but the hot idle pressure is still consided OK at I believe it was 0.3 bar; about 4.35 psi.
Your, gauge will not accurately read 0.3 bar.