Construction questions are marked by measurement, not just by eye — examiners check finished drawings against a tolerance of about $\pm 2\text{ mm}$ and $\pm 2^\circ$. Every mark on the page must come from a ruler, a protractor, or a pair of compasses — never estimated by "it looks about right."

Lines are measured with a ruler to the nearest millimetre, reading from the $0$ mark, not the edge of the ruler itself. Angles are measured with a protractor, placing its centre-cross exactly on the vertex and its baseline exactly along one arm of the angle, then reading from $0^\circ$ along that same arm around to the other arm.

To construct triangle $ABC$ with $AB = 7\text{ cm}$, $BC = 5\text{ cm}$, $CA = 6\text{ cm}$, using only a ruler and compasses:

1. Draw the longest side first with a ruler: $AB = 7\text{ cm}$.
2. Open the compasses to $6\text{ cm}$ ($CA$). Put the point on $A$ and draw an arc above the line.
3. Open the compasses to $5\text{ cm}$ ($BC$). Put the point on $B$ and draw an arc crossing the first.
4. Label the crossing point $C$, then join $AC$ and $BC$ with a ruler.

Drawing the longest side first, flat along the bottom, gives the two compass arcs the best chance of crossing cleanly above the line, which keeps the whole construction tidy and easy to check.

Perpendicular bisectors and angle bisectors are not required at Core tier. The only construction skill needed beyond a single triangle is building a compound shape from two such triangles, e.g. constructing a rhombus by drawing two congruent triangles back-to-back along a shared side — each triangle uses the rhombus's diagonal as one side, and its two equal edges as the other two.

A net is a 2D shape that folds up into a 3D solid. To draw one, picture "unfolding" the solid along its edges: a cuboid's net is six rectangles arranged in three matching pairs; a triangular prism's net is two triangular end-faces plus three rectangles, one per side of the triangle, each rectangle's width equal to the prism's length.

Worked example. The net of a closed cuboid box has a $6\text{ cm} \times 4\text{ cm}$ base, and the box is $3\text{ cm}$ tall. Find its total surface area.

A cuboid net unfolds into 3 pairs of identical rectangles:

Worked example. A closed triangular prism has length $10\text{ cm}$. Its triangular cross-section is right-angled with the two shorter sides $3\text{ cm}$ and $4\text{ cm}$, and hypotenuse $5\text{ cm}$. Find its total surface area.

Two triangular ends: $2\times\left(\frac{1}{2}\times3\times4\right) = 2\times6 = 12\text{ cm}^2$. Three rectangular faces, one per side of the triangle, each $10\text{ cm}$ long: