Attributes with Units

Numeric attributes may or may not have units. If an attribute has a unit such as meters, you can enter values using any distance unit from millimeters to light-years, and they will be converted to meters. You can change the units of an attribute to a different commensurate unit, and all its values will display with the new unit. But if you change the unit to something incommensurate (e.g., meters to years), all the values will become invalid.

If the value for an attribute for a particular case has an incommensurate unit, that value will be marked as invalid and will not be plotted in graphs. (see the value for age for case 3 at right.)

Numeric values without units are just numbers. Numeric values with units are quantities and are profoundly different from numbers. For example, 2 + 2 = 4, but 2 meters + 2 feet = 2.6096 meters. Using units with your data can really help you understand what the data mean, but the presence of units also makes Fathom a lot pickier (e.g., refusing to graph two attributes on the same axis because their units are incommensurate).

Among the units that Fathom knows about are some important physical constants that you can use as units, such as Earth masses (1 Earth mass = 5.9742 x 10^24 kg) or electron charges (1 electron charge = 1.602176462 x 10^-19 Coulomb).