For scientists & engineers only.
While Units can do simple conversions like mm to inches, it can do much more. Units actually performs dimensional analysis, keeping track of what dimensions certain units are in. For instance, attempting to convert pounds (force) to kilograms (mass) will give you an answer in terms of acceleration, just as Sir Isaac Newton said it would. (Multiply kg by g to get a kilogram's force on Earth).
Unlike free online unit converters, Units lets you expand its default database of dimensions, physical constants and astronomical observations by adding the ones that are useful to you and modifying its existing units to meet your conventions. It's always available in your pocket, instead of pulling out your web-enabled mobile device to realize your lab walls blocks most wireless internet access.
Units also gives you symbolic keyboard support that the iPhone's built-in keyboard does not offer.
• Dimensional analysis
• Database of most popular units, physical constants, astronomical observations
• Customize dimensions & units
• Extra symbolic keyboard
• Correct "offset" (temperature) support