The main bearings on your crankshaft are beginning to wear out excessively.
Oil level and oil pressure are different. You don't need to have full oil to get normal pressure.
Oil pressure has to built up. As long as the pressure is normal and the oil level is good. There is no problem.
It is normal for the pressure to drop. It depends what you mean by "very low". Check the oil level and the condition of the oil and filter. The oil and filter may need changing.
standard atmospheric pressure at sea level is 14.73 psi Absolute pressure is a gauge plus atmospheric pressure. The gauge being something that you are detecting.. i.e hot water tank.
Sea level.
Gauge pressure = absolute pressure - atmospheric pressure. Atmospheric pressure (at sea level) is generally taken to be 101.325kPa. so the answer is (C) = 448.955 kPa
Psig (pound-force per square inch gauge) is a unit of pressure relative to atmospheric pressure at sea level. By contrast, psia measures pressure relative to a vacuum (such as that in space). Most pressure gauges, such as tire gauges, are calibrated to read zero at sea level, because most applications require the difference of pressure. At sea level, Earth's atmosphere actually exerts a pressure of 14.695948804 psi. If a pressure gauge is calibrated to read zero in space, then at sea level on Earth it would read 14.695948804 psi. Thus a reading of 30 psig on a tire gauge, represents an absolute pressure of 44.695948804 psi.
------------>[bourdon tube]--------->[level & gear]---------->[pointer,scales]-------> pressure small amplified pressure displacement displacement
Zero (0) gauge pressure equals 14.696 PSI on the absolute scale. A lot of people will round up to 14.7 PSI for simplicity. 14.696 PSI is the pressure that is developed at sea level due to the weight of our atmosphere. The absolute pressure scale is based on zero being a perfect vacuum. Gauge pressure takes into account the atmospheric pressure at sea level (14.696 PSI). A simple conversion formula is PSIG+14.696=PSIA.
Atmospheric pressure is measured by a barometer and expressed in millibars. Normal atmospheric pressure at sea level is 1013 millibars.
120/80 mmHg
25 pounds per square inch is about 1.7atm