Flexible, easy to use, effective... all the things you want in science software are in this powerful little program. Metric Master will do, as its name suggests, just about any conversion you can think of. Measurements of distance, currency, mass, time are all here wrapped up in a simple and intuitive interface.

The original version of this program, ConvertUnits Pro, was a very good program as well, but suffered from a outdated interface. MetricMaster cures the eyesore problem, but also sports a wealth of features:

• 1000+ measurement units organized hierarchically in 100 groups (Length, Volume, Area, Force, Pressure, etc.) and nine categories (Basics, Electricity, Heat, History, Mechanics, Light & Radiation, Time, Unit Costs & Quantities, and Whimsy).
• Over 120,000 different conversions are possible.
• Definitions instantly available for any selected unit or unit group.
• Built-in (editable) links to major metric sites on the worldwide web for quick in-depth reference
• Commonly used compound units such as: tons, pounds, and ounces, hours, minutes, and seconds, and feet, inches and fractions
• 58 physical constants such as: speed of light and gravitational acceleration.
• Convert clock times between any two of over 200 locations in the world, in standard or 24-hour format
• Trivia conversions in the Whimsy category, to answer such important questions as: How many times higher is Mount Everest than the Washington Memorial?, or How much would I weigh on Jupiter?
• Currency conversions
• Significant figures vs. calculator display.
• U.S./English vs. International number formatting (commas vs. spaces).
• Scientific vs. standard notation.
• Record complete conversions (original value and unit name with converted value and unit name) in built-in journal, or save conversions to text files that can be opened and edited by most spreadsheets and word processors
• Compact view to show only units and values for repeat conversions for convenient cutting and pasting into open documents in other applications
• Customized conversion table generation
• Easily add and remove units from the database
• Store up to 30 often-used conversions in a pull-down menu for quick access.
• Comprehensive on-line help with insights on the history and methodology of measurement.

I tried out many of these features and they all work well. Maybe I'm losing my sense of humor in my old age, but the whimsy category seems a little much and unnecessary. I also like the new improved interface, but it still looks a little clunky to me. One other thing that bothers me is having to press the tiny "=" sign to see my conversion calculated - is this not just an unnecessary mouse click? Why can't the conversion just show up in the window?

Minor details aside, if you need a unit converter, you really need to consider this excellent product. If I were you, I'd download the "lite" version right now and give it a try - then fork over that $20!