They are given this status because they are useful in many practical everyday applications but are not strictly necessary for pure scientific and engineering work. They are however highly compatible and so do not detract from the advantages of metric, in fact they are very handy and user friendly. Again only select few are shown.
| Unit name | Symbol | Definition and what is measured |
|---|---|---|
| minute | min | Time = 60 s |
| hour | h | Time = 60 min = 3 600 s |
| day | d | Time = 24 h = 86 400 s |
| hectare | ha |
Area = 100 a = 10 000 m2
Used for land areas
|
| litre | l or L |
Volume = 1000 cm3 = 0.001 m3 = dm3(decimetre cube)
The familiar litre in which we buy petrol, etc. Note that (for all practical everyday purposes) 1 litre of pure liquid water weighs 1 kg
|
| tonne | t |
Mass = 1000 kg
Used in transport, vehicle masses and weight limits, etc. Also the approximate weight of a cubic metre of water (see litre above)
|
| bar | bar |
Pressure = 100 kPa
Used in weather mapping (mbar)
|