Help with Xfactor
- What's it for?
Dimensional analysis or factor-label method is a process
for converting known information into desired units, by multiplying or
dividing value+unit terms until all units except the desired ones
have canceled out, by appearing in both the numerator and denominator
(top and bottom) of the equation. It can be used for simple units
conversion (how many minutes in a day?) or complicated word problems
(see Examples). It can also verify
that a formula is dimensionally correct. Factor-label conversions
commonly come up in chemistry, engineering, and programming tasks.
- How's it work?
Start by entering the desired units on the left-hand side. Then
add known information on the right-hand side as units or
value units (separated by a space), so that intermediate
units cancel out. To add another term, click on the last (gray) "×".
To remove an unwanted term, click on the preceding (black) "×".
If you entered a term upside-down, just click on the divider line
to flip it around.
As you enter information, Javascript code scans the formula and
checks for any units that cancel out, showing them in green.
It also accumulates the numeric terms. Once the remaining
units match on the left and right side, the equals signs
change from red to green indicating that the final answer
has been reached.
- How do I...
- ... use compound units? Everything after the last
space is considered a unit. We suggest you hyphenate compound
units, e.g. "foot-lbs", or use abbreviations, e.g. "Nm", but
the important thing is just to be consistent so the automatic
matching will work.
- ... include variables? You can include symbolic
variables in the terms, with or without numbers, before the last
space separating the value from the units. These variables
are carried into the final result, to give you a simplified
conversion formula rather than a simple number.
See example 2.
- Where can I learn more?
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