I am in university studying biology and am supposed to plot a graph of how the absorbance of an endospore in different conditions changes with time. The data from 4 different groups was pooled: each pair took 2 different flasks of medium and found its absorbance every 20mins until the endospores changed into active cells. So all in all there was 8 different flasks (8 different lines on a graph needs to be plotted)

However, it says in my manual on how to write up this report that the lines on the graph need to start at the same point on the graph. However, when plotting absorbance against time the data don't start at the same point e.g.
Flask 1 at time zero had an absorbance of 0.085
Flask 2 " " 0.083
Flask 3 " " 0.081
Flask 4 " " 0.081
It is claimed that this is very simple to do but I don't have a clue how to make them all begin at the same point on the graph. :mad:
Any help would be appreciated (also the graphs are expected to be done on excel, if this helps)
Thank you sooo much for your help

I don't know if this is right, it is just an idea:

Was the first reading equivalent to a background absorbance? If so you can take it away from all readings and then the first for all will be zero.

This might not be relevant, I don't know the intricacies of your experiment.

Im not quite sure what you mean by background absorbance?

In this particular experiment endospore was added to the flasks containing different mediums (the experiment was trying to find the mininal requirements for germination and outgrowth) and then an absorbance was taken straight away, the flask was then put in a 30 degrees Celsius shaking water bath. The absorbance was taken every 20 minutes after this.

Would this be classed as a background absorbance?