80 cm is a measure of the length of a physical quantity in MKS (meter, kilogram, and second) unit system. Inch also is unit that measures length in FPS system (foot, pound, and second) system. For understanding and communication purposes a unit conversion factor is used to convert one unit to another unit system.
The brain is to be taught by a learning process to understand the physical quantity (physical property) than can be quantified. Length is a physical property that quantifies a certain distance. Unit quantifies the length by using a standard measurement system like MKS.
Examples of physical properties are: length, mass, weight, electrical charge, boiling point, melting point, freezing point, frequency, density, area, volume heat, etc. The physical property volume of a substance means the space it occupies. It is quantified by using a unit like m3 (m.m.m) where m is the unit of length. Volume is a three dimensional physical property which has length, width, and height. The unit of length is m (meter). The same is true for width and height. Thus the unit of volume is m multiplied three times (mxmxm = m3). Frequency, a physical property) is the repetition of some action in one time unit like sec. When an ant moves around a circle once it has completed one cycle. If the ant does repeat the same many times then frequency is cycles per sec (number of cycles the ant completes in one second).
Once the physical property and the corresponding unit are standardized then the brain understands the physical property and it's measurement and communicates with others using the measurement unit.
Different people, different country may have different standards of measurement. International and most of the scientific community use metric system (MKS). USA uses the foot pound second (FPS) system. In order to do trading like buying steel pipe from a country of different measurement system for length and currency one has to use conversion factors for length as well as currency.
Calculation of conversion factor for length and currency:
Conversion from cm length to inch length:
1 inch = 2,54 cm; Then 80 cm = 1
= 80 cm x ---- x 1 inch
= 80/2.54 inch
= 31.496 inch
The conversion factor from inch to cm is 2.54
The money conversion factor varies daily and is available from web pages. The length conversion factor is constant. In this high tech world it is very easy to convert cm to inch using web pages. Web page needs the input length in cm unit and then it displays the corresponding length in inch unit