The best thing you can do is to start by changing the oil and oil filter.
Put the correct quantity of fresh oil in the engine (taking into account the filter change) that is specified by the manufacturer.
Then dip the dipstick and see where the oil level comes to.
If you dont get a reading then you have the wrong dipstick for the car.
Make a note of the engine number and go to your local Vauxhall dealer and get the correct dipstick.
Or
Go to a scrap yard with the car and try different dipsticks till you find one that indicates that (following oil renewal) oil is at max level.
Maurice
April 2011