You can insert the result of the previous conversion using the underscore (‘_’). It is useful when you want to convert the same input to several different units, for example
You have: 2.3 tonrefrigeration You want: btu/hr * 27600 / 3.6231884e-005 You have: _ You want: kW * 8.0887615 / 0.12362832
Suppose you want to do some deep frying that requires an oil depth of 2 inches. You have 1/2 gallon of oil, and want to know the largest-diameter pan that will maintain the required depth. The nonlinear unit ‘circlearea’ gives the radius of the circle (see Other Nonlinear Units, for a more detailed description) in SI units; you want the diameter in inches:
You have: 1|2 gallon / 2 in You want: circlearea 0.10890173 m You have: 2 _ You want: in * 8.5749393 / 0.1166189
In most cases, surrounding white space is optional, so the previous example could have used ‘2_’. If ‘_’ follows a non-numerical unit symbol, however, the space is required:
You have: m_ ^ Parse error
When ‘_’ is followed by a digit, the operation is multiplication rather than exponentiation, so that ‘_2’, is equivalent to ‘_ * 2’ rather than ‘_^2’.
You can use the ‘_’ symbol any number of times; for example,
You have: m You want: Definition: 1 m You have: _ _ You want: Definition: 1 m^2
Using ‘_’ before a conversion has been performed (e.g., immediately after invocation) generates an error:
You have: _ ^ No previous result; '_' not set
Accordingly, ‘_’ serves no purpose when units is invoked non-interactively.
If units is invoked with the --verbose option (see Invoking Units), the value of ‘_’ is not expanded:
You have: mile You want: ft mile = 5280 ft mile = (1 / 0.00018939394) ft You have: _ You want: m _ = 1609.344 m _ = (1 / 0.00062137119) m
You can give ‘_’ at the ‘You want:’ prompt, but it usually is not very useful.