Spreadsheets that Calculate
Charts from a spreadsheet
Choose the kind of chart a set of numbers needs, and read amounts and shares off the chart that results.
A chart turns a column of numbers into a shape you can take in at a glance, and the reason there is more than one kind of chart is that a glance can only answer one question at a time. A bar chart answers which of these is biggest. A line chart answers what happened next, over and over, so it wants numbers that come in an order somebody cares about. A pie chart answers how one whole thing was divided up. Choosing a chart is really choosing which of those three questions you want the picture to shout, and a set of numbers that does not suit a question will make a chart that looks fine and says nothing.
Where the scale starts is part of the picture
A bar is as tall as the distance from the bottom of the scale up to its value — not from nothing up to its value, unless the scale happens to start at nothing. So two charts drawn from the very same numbers can leave two completely different impressions, and moving where the scale begins is all it takes. This is worth checking every single time you read someone else's chart: find the bottom of the upright scale before you look at the bars, because until you have, you do not yet know what you are looking at.
Worked example
Thirty children were asked a question and 10 of them said yes. How big is the yes slice on a pie chart?
First find the share: 10 out of 30 is one third of everybody asked.
Working in shares rather than in people is what makes the next step possible, because a circle knows nothing about people.
Try it together
Now read a chart together. It is drawn from C2:C7, one bar for each cell, and those cells hold 14, 9, 22, 9, 17 and 5.
Work from the cells, and check each answer against the picture you would expect.
1.How many bars does the chart have?
Have a go
Have a go on your own. A pie chart is drawn for 40 people. How many degrees of the circle does a single person take?
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.