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# Re: [libreoffice-users] Graph with two sets of Readings in Calc

```Hi.
```
I don't know if you can insert a chart with a trend line that is forced through zero. The dialogue probably needs another tick box "Force through zero"
```
```
In this case you can add an extra column to calculate the straight line. You can use the function LINEST to calculate the straight line that fits data y1 and passes through the origin. You can then insert a chart, xy, lines and points and have the series y1 and the straight line fitted to y1 and the series y2.
```

```
I can also derive another meaning to your question which may not be as you intend, but is something we do to show errors. We plot y1 against x with y1 on the left axis. We calculate the straight line fit for y1. We then calculate the error that y2 is from the straight line and plot that error (deviation from the straight line) using an expanded scale on the right y axis.
```Steve

On 2013-04-01 15:55, Gulzar Singh wrote:
```
```
Yes.  Concentration values are same for both.
```
Standard readings will create a straight line from origin with two or more values. On that line values of sample are to be plotted. Now that point will be used to determine concentration of sample.
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```
On Apr 1, 2013 8:19 AM, "Steve Edmonds" <steve.edmonds@ptglobal.com <mailto:steve.edmonds@ptglobal.com>> wrote:
```

On 2013-04-01 14:13, Gulzar Singh wrote:

I have two group of readings. First called as "Standard".
Second as
"Sample". Each group has 6 readings. I need to create a graph.
X-axis with
'concentration'. Y-axis with 'OD'. PROBLEM: Standard readings
should be
plotted first and a straight line from origin with any two or
should be made. Now on that line values of sample are to be
marked.
How to do it ? Need it for project .Urgent.

Hi.
Is the x value for concentration the same for both sets of readings.
e.g.

x       y1       y2

0       0.05     0.06

0.1     3.0      2.9

0.19    5.9      6.1

0.29    9.1      9.2

0.41    12.2     12.3

0.5     15.02    15.4

Steve

```
```

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