Interactive protractor for the whiteboard

What the interactive protractor does on screen

There are two modes, and the button for them sits at the top left. Show draws a protractor across the whiteboard with an angle already sitting under it, so the class can get straight to reading the scale. Measure draws the angle on the board on its own and hands you the protractor to place.

• The angle. Two black arms meet at a dot in the middle of the straight edge. The white dot sits on the fixed arm, the yellow dot on the moving one. Drag the yellow dot and the angle opens and closes a degree at a time.
• Set. Type a size into the box and press Set, and the angle swings round to it. That is how you land on 137 without pressing plus ten fourteen times.
• The tilt. Drag the white dot and the whole angle swings round, so it can sit at any slant rather than always resting along the bottom. The two Tilt buttons turn it fifteen degrees at a time, one each way.
• The scale. A tick for every degree, a longer one every five, a longer one again every ten. The outer numbers count up one way and the smaller grey numbers underneath count the other way, so both scales are genuinely there to choose between.
• Nudging. The minus ten, minus one, plus one and plus ten buttons change the angle exactly, with the current size shown between them. That is how you land on precisely 90 or 180.
• The reading. Under the protractor, the size in degrees and its name: acute, right angle, obtuse, straight or reflex.
• Hide reading. Turns the size into a question mark both under the board and in the controls, so nothing on screen gives it away. Press it again to reveal.
• Random angle. A new size at a new tilt, ready to be measured. With Hide reading on, that is a whole starter and it took you one press.
• Reflex. Swaps the half protractor for a full circle marked all the way to 360, for angles bigger than a straight line. The button then reads Semicircle to bring you back.
• Measure mode. An angle appears on one side of the board and the protractor parks on the other. Drag the protractor by its body until the middle of its cross sits on the point of the angle, then drag the white dot to swing the zero round onto one arm. The whole protractor turns green the moment it is properly lined up, and a ring pulses at the point.
• Draw. Acute, obtuse, reflex or mixed. Whichever you pick, New angle draws another one, opening out from nothing so the class watches it being made. A reflex angle brings the full circle up on its own.
• Estimate and Reveal. Type the number the class has agreed on, press Reveal, and it reads back: you said 60, it is 65, five out. Leave the box empty and Reveal just gives the size and its name.
• Snap. On, the protractor jumps the last few millimetres onto the point and the last few degrees onto the arm, which is kind on a whiteboard pen. Off, it has to be placed by hand, which is the harder and more honest version.
• Reset and Print. In Show, Reset goes back to 50 degrees sitting flat with the reading showing. In Measure, it draws a fresh angle and sends the protractor back to its parking spot. Print gives you one A4 landscape picture of the board as it looks.

How to use it in a lesson

Teach the reading before you teach the placing. On paper, children lose marks for lining the protractor up badly and for choosing the wrong scale, and those are two separate problems. Start in Show, where the protractor is already in the right place and the whole lesson can be about which number to read. Move to Measure once that is secure, and the only thing left to get wrong is the placing.

1. Press Random angle, then Hide reading. Do it in that order or the class sees the number as it lands.
2. Everybody estimates first, on a whiteboard or in a book, before anyone touches the scale. Acute or obtuse, then a number.
3. Send one child out to measure it and say which of the two numbers they used and why. That sentence is the actual objective of the lesson.
4. Reveal it and compare with the estimates, then press Random angle and go round again, faster.
5. Prove the tilt does not matter. Set an angle, read it, press Tilt four or five times and read it again. Same number, upside down.
6. Land on the benchmarks. Use the plus ten and plus one buttons to hit exactly 90, then 180, and name what you have got. Children estimate badly until those two are fixed in their heads.
7. Then switch to Measure and hand it over. Estimate first, type it into the box, and only then let a child come up and place the protractor. Snap on for the first few, off once they are getting it.

One thing worth knowing before the board is live: nothing moves unless you take hold of a dot or of one of the arms, so a hand resting on the protractor cannot change the reading by accident.

Ideas by year group

• Year 1. Reset, then drag the yellow dot slowly round and back. Bigger and smaller, opening and closing. No numbers at all yet.
• Year 2. Nudge it to 90 and call it a corner. Then open and close it, asking each time whether it is bigger or smaller than that corner.
• Year 3. Drag slowly and have the class shout stop when it passes the right angle. Then name what you have got: acute or obtuse.
• Year 4. Nudge to 90, then 180, then Tilt it right over. A quarter turn and a half turn. How many degrees in a whole turn, and how do you know?
• Year 5. Measure mode with Snap off. Estimate into the box, place the protractor, Reveal, and justify which of the two scales you read and why that one.
• Year 6. Draw set to Reflex. Place the full circle, read the reflex angle, then ask for the angle inside as well and what the two make together.

The misconceptions it helps with

Reading the wrong scale. The big one. An angle of 60 also has 120 printed beside it, and the only way to choose is to start from the arm sitting on zero. Hide the reading, take two answers, and let the class argue it out.

An angle turned round is a different angle. Tilt it right over so both arms point oddly and ask whether it has changed. The reading says no, which lands better than being told.

Estimating with nothing to estimate against. Setting 90 and 180 exactly, and looking at them, gives an anchor for every guess that follows.

Putting the protractor down anywhere near it. In Measure, close is not good enough: the cross has to be on the point and the zero has to be on an arm, and it only goes green when both are true. Turn Snap off and the class can see how fussy that is.

Measuring the wrong side of a reflex angle. In the full circle an angle of 250 is plainly the long way round. Ask for the angle inside as well, and the fact that they make 360 comes out of the picture rather than out of a rule.

Frequently asked questions