Measures

• Read scales by working out what one small division is worth.
• Convert between the 12-hour clock (am/pm) and the 24-hour clock, and find time intervals.
• Make sensible estimates of lengths, masses and capacities.
• Three-figure bearings are measured clockwise from North; measure angles to the nearest degree.
• Speed = distance ÷ time; density = mass ÷ volume; pressure = force ÷ area.

Reading instruments; sensible values

On any scale, first find the value of one small division: (difference between two labelled marks) ÷ (number of divisions between them). Then count divisions from the nearest labelled mark.

For estimates, compare with things you know: a door is about 2 m tall, a bag of sugar has a mass of about 1 kg, a can of drink holds about 330 ml, an adult is about 1.7 m tall.

am, pm and time intervals

24-hour times always use four digits: 7:05 am = 07:05, 7:05 pm = 19:05, midnight = 00:00, midday = 12:00. To find a time interval, count up to the next whole hour, then whole hours, then the remaining minutes. Never subtract times as if they were decimals.

Three-figure bearings

A bearing is an angle measured clockwise from North, written with three figures: 045°, 160°, 300°. To measure, draw a North line at the point you are measuring from. Measure angles with a protractor to the nearest degree, using the scale that starts at 0 on one arm of the angle.

Average speed

Average speed = total distance ÷ total time. Times in hours and minutes must be changed to hours as a decimal or fraction: 15 minutes = 0.25 h, 40 minutes = 2/3 h.

Density and pressure