3 Replies Latest reply: Jan 30, 2014 2:00 AM by Barry
Level 1

Hello and thanks for taking time to read and answer my question.  So I have a science fair project coming up and numbers is being very annoying.  My experiment is testing the affect of temperature on the effectiveness of magnets.  My table looks like this:

 Magnet 1 Magnet 2 Magnet 3 Magnet 4 Magnet 5 Average 74 Degrees 40g 42g 50g 27g 38g 39.4 200 Degrees 28g 25g 35g 46g 38g 34.4 250 Degrees 62g 39g 10g 53g 29g 38.6 300 Degrees 34g 19g 36g 23g 41g 30.6 350 Degrees 26g 21g 17g 36g 37g 27.4

All I want to do is make a simple line graph that will show the correlation (or lack of one) However, when I try to make it into a graph, I keep either getting no lines at all or only the line for the average.  Why is this?  What am I doing wrong?  Help is greatly appreciated.

Thanks so much,

Colton

I'm using numbers 3.1 by the way.

• Level 6
Mac OS X

Hi Colton,

1. Your data are text, not numbers. Take out the g after each value.

2. for a line graph, Categories must be in a Header Column.

3. Row 2 is empty. Delete it.

4. Make Row 1 a Header Row.

You might want to adjust the number of steps on the Y axis to get sensible values for labels

Regards,

Ian.

• Level 6
Mac OS X

Hi Colton, Update.

Perhaps a 2D Scatter graph will better suit your data, as the temperatures are not evenly spaced.

2-D Scatter from the Chart button:

Here is the data table. I "cleaned up" the original data by copying and pasting into TextEdit, then copying and pasting into a new Numbers table (one Header Row but no Header Column, as required for a Scatter Plot).

Select Columns A to F (you can include the Average later if you like)

Choose Scatter Plot

The X axis now has evenly-spaced labels (more scientific ).

Click on the chart, then Format Panel > Axis > Value (Y)  > Axis Scale > Steps 7 (to get steps of 10 in this example).

Regards,

Ian.

• Level 7

Hi Colton,

"I keep either getting no lines at all or only the line for the average.  Why is this? "

It's because the column labeled Average is the only one containing numbers. Appending the g or " Degrees" forces Numbers to regard the values in the other columns as Text, which has no numerical value, and can't be graphed.

With the text stripped from those numerical values you can produce either of these two graphs. See the notes below regrding the major differences.

Scatter chart with connected points

Line chart

Cosmetically, the line graph appears with thicker lines connecting the data points, and with all symbols set to open circles. I thickened the connecting lines on the scatter chart to make them more visible, and made the Average line about 40% thicker than the others. No changes were made to the lines on the line chart.

The legend for both (Magnet 1, Magnet 2, etc.) appears as a horizontal line (or lines) of text. Selecting the box, then dragging either handle toward the other forces the labels into a vertical stack, which can then be moved to a visually better position.

The main functional difference between the two types is in the purpose of the X axis.

In the scatter chart, both X and Y axes are Value axes—the position of each data point is determined vertically by its Y value and horizontally by its X value.

The Line chart is a Category chart. Category charts have one Value axis (here the Y axis) and one Category axis (here the X axis). Categories are equally spaced along the Category axis, and the data points' vertical position(in this example) is determined by the Y value of the point.

In your case, the difference can be seen in the (horizontal) distance between the first two samples in each series compared to the (horizontal) distance between other ajacent pairs in the same series. In the Line chart, these distances are all the same. In the Scatter chart the first pair (74° and 200°) are more widely separated than the others (each 50° higher than the temperature before it).

In cases where you are trying to show a relationship (or lack of relationship) between two sets of values (speed vs braking distance, temperature vs volume, etc.) a scatter chart usually gives a better representation.

Practical note: Values must be placed in non-Header rows and columns. Labels, including Category labels, must be placed in Header Rows or Header columns to be picked up by the chart. The formatting of the pasted data in your initial post indicates the temperatures are in a Header column. The column labels are (and should be) in a Header row.

Regards,

Barry

PS: You might want to check the meanings of "affect" and "effect" before commiting yourself to either on your display and in your report.

PPS to Yellowbox: HI Ian. Looks like you got started earlier and/or wrote faster thn I did! Something odd happened in the example in your first post. The category labels have been offset one cata set to the right, and there's no 350.

B