Vectors and scalars
A scalar quantity (mass, speed, distance, time, energy) is fully described by a number and a unit. A vector quantity (force, velocity, displacement, acceleration) needs a direction too. Two vectors at right angles combine using Pythagoras' theorem.
Example 1: Two forces, 3 N and 4 N, act perpendicular to each other on an object. Find the resultant force.
.
Precision instruments
A vernier caliper has a main scale and a sliding vernier scale; the reading is the main scale value at (or just before) the vernier's zero, plus the vernier scale division that lines up exactly with a main scale mark, multiplied by the instrument's precision (commonly 0.01 cm). A micrometer screw gauge works similarly but measures much smaller lengths, reading a main (sleeve) scale plus a rotating thimble scale, with a typical precision of 0.01 mm -- useful for things like wire diameter or sheet thickness that a ruler can't measure accurately.
Example 2: A vernier caliper's main scale reads 2.3 cm just before the vernier's zero, and the 4th vernier division lines up with a main scale mark, with a precision of 0.01 cm. Find the reading.
Reading = main scale + (vernier division precision) = .
Why measurement precision matters
Every measuring instrument has a limit to how finely it can distinguish two close values -- using a tool with too little precision for the quantity being measured (e.g. an ordinary ruler for a wire's diameter) produces a result that looks confident but hides real uncertainty. JAMB often tests whether you can correctly read an instrument's scale, not just whether you know the formula that uses the reading afterwards.