Mass
The basic SI unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.
Mass spectrometry
There are several important analyser characteristics. The mass resolving power is the measure of the ability to distinguish two peaks of slightly different "m/z". The mass accuracy is the ratio of the "m/z" measurement error to the true m/z. Mass accuracy is usually measured in ppm or milli mass units. The mass range is the range of "m/z" amenable to analysis by a given analyzer. The linear dynamic range is the range over which ion signal is linear with analyte concentration. Speed refers to the time frame of the experiment and ultimately is used to determine the number of spectra per unit time that can be generated.