The TI-89 and TI-92+ calculators have a built-in unit conversion capacity.
You can find
the list of units the calculator knows on the UNITS menu.
The list is fairly extensive.
The format
is 1_m, for one meter. For an unknown number x of meters,
you enter x * _m.
The calculator
thinks of _m as a quantity or expression which is multiplied by
the number of meters.
You can
leave out the multiplication symbol with numbers (just as you can write
2y instead of 2 * y), but not with variables.
(The calculator
thinks x_m is a new variable with
a three-character name.)
If you would prefer to enter units by hand instead of going to the UNITS menu, remember that every unit name begins with an underline character, indicated on the keyboard pictures above.
Conversion
The default
unit system is SI, also known as MKS, for meter, kilogram, second.
(You can
change this to English or to a custom system you define yourself using
the MODE menu.)
If you enter units in some other system, the calculator automatically converts to the default system.
If you want to convert to units which are not included in the default system, you need the convert symbol, a triangle also marked on the keyboard pictures above. (You use the same symbol for converting from rectangular to polar coordinates.)
Also observe that the calculator knows how the common units within a given system are related. The next-to-last line on the history screen above shows that the calculator knows that a Newton-meter is a Joule.
The abbreviation for a pound of force in the English system is _lbf. The calculator treats _lb as a unit of mass.
The usual conversion utility does not work for temperatures.
Apparently
the calculator automatically assumes the degree symbol refers to angles.
To convert
temperatures, use the tmpCnv command, in the CATALOG
under T.
To convert
temperature ranges (a difference of 20 degrees Celsius is how many degrees
Farenheit?) use
DtmpCnv,
which is also in the CATLOG, also under T.
You can attach
units to any number or variable on the HOME screen,
in the Data/Matrix Editor, etc.
This gets
you into trouble on the GRAPH screen, and can confuse
you in other circumstances.
For example,
since x meters is the product of the variable x and the variable
_m, you can't integrate with respect
to x meters.
You can
integrate with respect to x for x between 0 and 1_m.
(Note that
0 and 0_m are the same thing, since the calculator treats
0_m as a product.)