<P> The Australian building trades adopted the metric system in 1966 and the units used for measurement of length are metres (m) and millimetres (mm). Centimetres (cm) are avoided as they cause confusion when reading plans . For example, the length two and a half metres is usually recorded as 2500 mm or 2.5 m; it would be considered non-standard to record this length as 250 cm . </P> <P> American surveyors use a decimal - based system of measurement devised by Edmund Gunter in 1620 . The base unit is Gunter's chain of 66 feet (20 m) which is subdivided into 4 rods, each of 16.5 ft or 100 links of 0.66 feet . A link is abbreviated "lk," and links "lks" in old deeds and land surveys done for the government . </P> <P> Time is an abstract measurement of elemental changes over a non spatial continuum . It is denoted by numbers and / or named periods such as hours, days, weeks, months and years . It is an apparently irreversible series of occurrences within this non spatial continuum . It is also used to denote an interval between two relative points on this continuum . </P> <P> Mass refers to the intrinsic property of all material objects to resist changes in their momentum . Weight, on the other hand, refers to the downward force produced when a mass is in a gravitational field . In free fall, (no net gravitational forces) objects lack weight but retain their mass . The Imperial units of mass include the ounce, pound, and ton . The metric units gram and kilogram are units of mass . </P>

What do the small lines on a ruler mean