# Figure of merit

A figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. In engineering, figures of merit are used as a marketing tool to convince consumers to choose a particular brand.

## Examples

Benchmarks are synthetic figures of merit that summarize the speed of computers in performing various typical tasks. Benchmarks designed by a manufacturer generally rate the manufacturer's products more favorably than benchmarks designed by others or by independent benchmarkers.

## Modulation Systems

In modulation systems for communication, figure of merit of a device means the ratio of output Signal to Noise Ratio to the input Signal to Noise Ratio.

### Amplitude modulation

Figure of merit for Amplitude modulation is given by

$\mathrm{\frac{(SNR)_{O,AM}}{(SNR)_{C,AM}}}=\frac{k_a^2P}{1+k_a^2P}$

Figure of merit for DSB-SC receiver or that of an SSB modulation is always unity. Therefore noise performance of AM receiver is inferior to that of a DSB-SC receiver or an SSB receiver.

### Frequency modulation

Figure of merit for Frequency modulation is given by

$\mathrm{\frac{(SNR)_{O,FM}}{(SNR)_{C,FM}}}=\frac{3k_f^2P}{W^2}$

## Deception

The precision and verifiability of numbers sometimes make them a more effective sales tool than vague and non numeric descriptions such as "state of the art" or "leaves the others in the dust". When used in deceptive advertising, the deception lies more in the question of relevance rather than truth since the number quoted as a figure of merit may not be enough to determine performance when comparing products. For example, when purchasing a laptop a consumer could choose based on the capacity of its hard drive. The RPM, buffer, and seek times may not be noted, but significantly affect performance.

Some figures such as Peak Music Power are used in selling consumer merchandise and have the principal merit of yielding high numbers that can impress people who don't know what the numbers mean. Other figures such as Specific Fuel Consumption are addressed to engineers and other studious buyers whom the sellers dare not mislead.

Another example is the megapixel count of a digital camera. A consumer unaware that the number of pixels on a sensor is only one factor in the quality of the image that is captured may, for example, buy a camera with more pixels squeezed onto a small image sensor, thus losing quality to small pixels.

Makers of cheap, consumer-market telescopes often tout the magnification power of their products, sidestepping the fact that aperture, optical quality, and the type and quality of the telescope's mount are of more importance in obtaining a quality image.