Somebody asked about the size of barrels, the standard water drum is 55 gallons, however, when you are talking about the output of oil, it varies depending on what grade of oil, who is talking about it (US, Europe or mid east) and what time of year it is (a barrel is bigger in the summer, than the winter, or at least they used to be)! Deopending on the above factors, the actual size varies between 40 and 80 gallons.
Mass/Weight: In geology, minerals are rated by their SG or specific gravity. This is a measure of their mass compared to an equal volume of water (typicaly 1 cubic meter, or 1 cubic centimeter) This has the handy property that on Earth, water masses 1g/cm or 1Kg/m. For instance, Heamatite, an ore of iron, has an SG of 5.26, making it 5.26 times heavier than an equal volume of water and a cube 1cm on a side 5.26g and a kube 1m on a side 5260kg, or 5.26 tons. Very handy. As its a ratio compared to water, it is unitless, and will not be modfified to by local gravity. Heamatite will have an SG of 5.26 under 1G coditions or 10G conditions.
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