dcf.cymru stimulus sheet · Design Technology · Year 8

The new computer room: body data, guidance and a class log

Three sources for one design job. The school, the pupils and the class log are invented. The body measurements are rounded illustrative figures made for this lesson, not a published data set. The healthy-use guidance is based on Health and Safety Executive (HSE) advice on display screen equipment.

The brief

Ysgol Bryn Hafod is fitting out a new computer room for 30 pupils. The Design Technology department has been asked to set the adjustment ranges for the new chairs, desks and monitor arms, so that the room suits pupils aged 12 to 14. The furniture must fit at least 90% of pupils without any help.

A. Body data for pupils aged 12 to 14

All measurements are in millimetres (mm), taken sitting upright, with school shoes on. Illustrative figures for this lesson only.

Measurement	5th percentile	50th percentile	95th percentile
Knee-to-floor height (popliteal height): floor to the back of the knee	370	410	450
Sitting elbow height: top of the seat to the underside of the elbow, upper arm hanging down	180	215	250
Sitting eye height: top of the seat to the eye	650	720	790
Forearm reach: back of the elbow to the tip of the middle finger	380	420	465

Reading a percentile: the 5th percentile knee-to-floor height is 370 mm. That means 5% of pupils aged 12 to 14 have a knee-to-floor height below 370 mm, and 95% have one above it.

B. Healthy-use guidance

HSE guidance is written for people at work, but the same advice suits pupils using computers in school.

Seat: set the seat height so that your thighs are supported along their length and roughly level. Your feet should rest flat on the floor; if they cannot, use a footrest. The front edge of the seat should not press into the back of your knees.
Desk and keyboard: the keyboard should be just below elbow height, so your forearms are roughly horizontal and your wrists are straight. Leave a space in front of the keyboard to rest your hands. Keep the mouse close, in line with your elbow, so you do not stretch for it.
Screen: directly in front of you, about an arm’s length away, with the top of the screen at about eye level (level with your eyes or slightly below). A laptop used for a long time should be raised on a stand, with a separate keyboard and mouse.
Light: avoid glare and bright reflections. Place the screen so it does not directly face a window or a bright light; side-on to the window is usually best. Use blinds to cut out strong sunlight.
Breaks: take breaks or changes of activity. Short, frequent breaks are better than long, rare ones: for example, 5 to 10 minutes every hour is better than 20 minutes every 2 hours. Stand up, move around, stretch, and look into the distance from time to time.

Ysgol Bryn Hafod room rule (invented for this lesson): stop for a break or change of activity of at least 5 minutes before you have been on a screen for more than 50 minutes. A stretch of exactly 50 minutes keeps the rule; anything longer breaks it.

C. Class log: one day of screen time (invented)

Ten pupils in class 8B kept a log for one Tuesday. Total screen time includes lessons, homework and free time. Longest stretch is the longest time they spent on a screen without a break of at least 5 minutes. All times are in minutes.

Pupil	Total screen time (min)	Longest stretch without a break (min)
Aled	180	40
Bethan	240	55
Cai	150	30
Deio	420	95
Elin	200	45
Ffion	160	35
Gethin	210	50
Hana	190	25
Iestyn	230	60
Lowri	170	40

Under the table, the class representative wrote: “The mean longest stretch is 47.5 minutes, which is under 50, so our class keeps the break rule.”