Use of SI units requires special care, more particularly in writing prefixes.
Following points should be kept in mind while using units.
The symbol of unit named after a scientist has initial capital letters such as N for Newton.
The prefix should be written before the unit without any space, such as 1× 10^{ˉ³} m is written as 1 mm.
A combination of units is written each with one space apart. For example, Newton meter is written as N m.
A number such as 5.0 × 10^{⁴} cm may be expressed in scientific notation as 5.0 × 10² m.
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, 1 km² = 1 (km) ² =1 × 10⁶ m².
Measurement in practical work should 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 result, all measurements must be converted to the appropriate SI base units.