Negative oil pressure
 

Saw it for the first time ever yesterday. On a GE90 right at initial engine start. Only went to -1 psi but was a little surprised that the manufacturer would even take the time to provide such a measurement.

Yup, quite common on the GE90s. Oil pressure as indicated on the EICAS is a differential measurement between the oil pressure after the oil/oil heat exchanger and the air pressure in the bearing sump, never seen anything lower than -1psi, so I would still reckon thats actually 0 delta p within the accuracy of the piezo pressure transducer elements.