Scientific Notation
International system of units – Numbers are expressed in standard form called scientific notation, which employs powers of ten. The internationally accepted practice is that there should be only one non-zero digit left of decimal. Thus, the number 134. 7 should be written as 
and 0.0023 should be expressed as 
Conventions for indicating units
Use of SI units requires special care, more particularly in writing prefixes.
Following points should be kept in mind while using units.
(i) Full name of the unit does not begin with a capital letter even if named after a scientist e.g., newton.
(ii) The symbol of unit named after a scientist has intial capital letter such as N for newton.
(iii) The prefix should be written before the unit without any space, such as 
m is written as 1mm. standard prefixes are given in table 1.4.
Table 1.4
Some prefixes for powers of ten
(iv) A combination of base units is written each with one space apart. For example, newton metre is written as N m.
(v) Compound prefixes are not allowed. For example, 1µµF may be written as 1pF.
(vi) A number such as 
cm may be expressed in scientific notation as 
m.
(vii) When a multiple of a base unit is raised to a power, the power applies to the whole multiple and not the base unit alone. Thus, 
(viii) Measurement in practical work be supposed to be recorded immediately in the most convenient unit, e.g. micrometer screw gauge measurement in mm, and the mass of calorimeter in grams (g). but before calculation for the end result, every measurements must be converted to the appropriate SI base units.