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# Convering 1:5 serial dilutions to logarithm scale for efficiency curves

Logarithm PCR

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### #1 Joe101

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Posted 12 April 2012 - 08:02 AM

Hello,

When plotting efficiency curves I understand you need to convert your dilution factor to a log then plot the CT numbers against this. Currently I have 5 dilution series of 1:5, so 1:5, 1:25, 1:125, 1:652 and 1:3125. I tried to do a log transform on the numbers of this in SPSS and it gave me 0, .7,1.4,2.1,2.8,3.49 which I dont think is right as I need the series to begin with 1.

I'm really quite stuck with this, can anyone help?

Many thanks,
Joe

### #2 Joe101

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Posted 12 April 2012 - 08:16 AM

Sorry, I just did the same calculation but with the lgn10 of the cDNA input rather than dilution factor and that looks alot more promising. I'm still not sure I've done the right thing though so any confirmation/further help would be great.

Thanks again,
Joe

### #3 Trof

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Posted 13 April 2012 - 07:21 AM

Since 10x dilutions are whole numbers, i.e. 1 (undiluted), 1/10, 1/100, 1/1000... meaning 1, 0.1, 0.01, 0.001 is 0, -1, -2, -3 in log scale.
then 5x dilutions are 1(undiluted), 0.2, 0.04, 0.008, ... is 0, -0.7, -1.4, -2.1 and so in log scale.
If you count undiluted as 1, then the log10 is always 0. So it starts with zero.

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### #4 newborn

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Posted 18 April 2012 - 10:01 PM

Logarithm of 5 can be used to get the integer number.