[10.3] Remove Units From Numbers; [10.4] Add Units To Undefined Variables; [10.5] Use Tmpcnv() To Display Temperature Conversion Equations - Texas Instruments TI-89 Tip List

If a conversion includes units other than these seven, it is not a base unit conversion.
(credit to anonymous poster)

[10.3] Remove units from numbers

Suppose x is a number with an associated unit, for example, 1.2_m. To extract just the numeric value,
use
part(x,1)
To extract just the units, use
part(x,2)
For example,
part(1.2_m,1)
part(1.2_m,2)
This also works for compound units, for example
part(1.2_m*_s/_mol,2)

[10.4] Add units to undefined variables

Units can be applied to variables and expressions, as well as to numbers. For example, to create a
variable tf with units of °F, use
tf*_°F
The important point is to explicitly multiply the variable name by the units. This is not necessary when
applying units to numbers. A domain error message results if you do not use the explicit multiplication.
The example above gives different results, depending on the value of tf:
If tf is undefined:
If tf is a number, like 12:
If tf is another variable name, like tf2:

[10.5] Use tmpcnv() to display temperature conversion equations

tmpcnv() usually performs temperature conversion on numbers, for example
tmpcnv(0_°C,_°F)
results in 32_°F. You can also use tmpcnv() to display the temperature conversion equations, if you
convert an undefined variable, like this:
returns 1.2
returns 1*_m
returns
tf·_°F
12·_°F
tf2·_°F
1$_m$_s
1$_mol
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