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1. Major problems with semilog paper
Hi,

I am trying to plot data on semi-log paper and having problems.

I am trying to plot the size of the DNA ladder fragments and the distance they migrated, i have two DNA markers so would they go on the same graph?
I know that distance will be on the x axis and size would be on the y axis.

Kbp marker
500bp 6.2cm
1000bp 5.3cm
2000bp 4.9cm
3000bp 4.6cm
4000bp 4.3cm
5000bp 4.1cm
6000bp 4.0cm
7000bp 3.8cm
8000bp 3.6cm

100bp marker

100bp 8cm
200bp 7.3cm
300bp 6.9cm
400bp 6.5cm
500bp 6.2cm
600bp 6.0cm
700bp 5.8cm
800bp 5.5cm
900bp 5.3cm
1000bp 5.0cm

This is the data above that needs to be plotted, but I dont understand where each of these would go on the paper, because the semilog paper starts from 1,2 etc up to 10, and then it goes in 20s, 30s, etc upto 100, and then 200,300 etc upto 1000, so where would I plot these figures

Sorry for the long post any help would be appreciated
2. Re: Major problems with semilog paper
You can plot both on the same graph, if you wish (use different colors or dots instead of crosses or something

The distance goes as normal on the Y axis.

The base code size needs to go on the log scale x axis. The most accurate way would be to have a normally spaced x axis that would go '1,2,3...' then plot log(x) on the graph, and label the x-axis values '1,10,100...' - log graph done. Having weird log paper always puts into question exactly where a value should go if its in the middle of two marked values, although with your values it should be fine. Where it says '100', plot the 100 point. Same for 200 and so forth. Does it not go above 1000? If not, you can extend the axis yourself if you feel up to it - the spacing between the '1000, 2000, 3000...' points needs to be exactly the same as between the '100, 200, 300..' - you can measure it out.
3. Re: Major problems with semilog paper
(Original post by nexttime)
You can plot both on the same graph, if you wish (use different colors or dots instead of crosses or something

The distance goes as normal on the Y axis.

The base code size needs to go on the log scale x axis. The most accurate way would be to have a normally spaced x axis that would go '1,2,3...' then plot log(x) on the graph, and label the x-axis values '1,10,100...' - log graph done. Having weird log paper always puts into question exactly where a value should go if its in the middle of two marked values, although with your values it should be fine. Where it says '100', plot the 100 point. Same for 200 and so forth. Does it not go above 1000? If not, you can extend the axis yourself if you feel up to it - the spacing between the '1000, 2000, 3000...' points needs to be exactly the same as between the '100, 200, 300..' - you can measure it out.
Ok, so the x axis already has 1,2,3 etc on it. But how do I label the x-axis values ?
And yes it does not go up to 1000, and theres no space for me to extend the thing
4. Re: Major problems with semilog paper
(Original post by Gamewizard)
Ok, so the x axis already has 1,2,3 etc on it. But how do I label the x-axis values ?
And yes it does not go up to 1000, and theres no space for me to extend the thing
Well, if it doesn't go above 1000 then you will have to draw your own graph, add your own label on the same graph above instead of below, have your results x10^-1 (kind of excessive - i'd do your own, although i don't know what whoever marking this will want).

Doing your own is easy - just do a normal graph (with evenly spaced x-values) but plot log(x) versus y. This will bring all of your values under 5 and have them on a log scale. You can either label the x-axis with log(x) (i.e. 1,2,3) or with the actual values (1, 10, 100)

Its kind of hard to explain - ii can't see what this 'log paper' you have - i hope what i said is clear.

EDIT: e.g. look at the graphs on this site http://mathsisinteresting.blogspot.c...mic-scale.html
Last edited by nexttime; 16-12-2010 at 17:20.