Volume, Weights, Pressure, Speed of Sound

Volume
1 US Gallon equals roughly 3.785412 Litres
1 Imperial Gallon = 4.546 Litres
1 Cubic Inch = 16.38706 CC

1 CC = 0.06102374 Cubic Inch
1 CC = 0.001 Litres
1 CC = 1.0 Millilitres
1000 CC = 1 Litre

10 litres of fuel 200 CC (Ml) oil   50 : 1 ratio
10 litres of fuel 100 CC (Ml) oil 100 : 1 ratio

Weights
Weights (kg per cubic metre)
Lead          11370 kg per m³
Water fresh  1000kg per m³
Water sea     1025kg per m³
Ice                  705kg per m³
Diesel             854kg per m³
Petrol             740kg per m³
Lube oil         920 kg per m³

Divide the above by 1000 to find weight per litre.
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Pressure
1 Bar = 14.50377 PSI
1 Bar = 100 Kilopascals
1 Bar = 1000 Millibars
1 Bar = 100000 Pascals
1 Bar = 1000000 MicroBar

1 Bar of pressure for every 10 Metres of depth in sea water
Or 14.5PSI for every 33 Feet (10.06 meters) of depth in sea water
(Both measurements are approximations but are very close)

1 Inch of water    249.08891 pascals
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Speed of sound

Speed of sound in sea water
In sea water the speed of sound on average is 1500 Metres per second, however it will vary slightly with temperature and salinity

In dry air at 0 °C (32 °F), the speed of sound is 331.2 metres per second (1,087 ft/s; 1,192 km/h; 741 mph; 644 kn). At 20 °C (68 °F), the speed of sound is 343 metres per second (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or a kilometre in 2.91 s.