shifting the graph

[talkative__]

Hi dear helpers
I have two groups of data that are done at the same time but because of the devices error there are few seconds difference between them. I want to shift the graphs so that the maximum and minimums be exactly at the same time. is there any way?

Cheers

[MrShorty]

It can be difficult to give specific suggestions with only a picture of the two signal curves to work from. The basic approach (which is not necessarily specific to Excel) that I would probably use would look something like:

1) Locate the desired reference point in each curve. Usually, I prefer to locate "start of peak" rather than peak apex, but I cannot be sure which reference point you would prefer. This might be the hardest part of programming something like this, especially if you want it to be fully automated so that it will correctly every time without user input. The algorithm will be some kind of "lookup" function that will be able to "find" and identify the "start of peak". I could be influenced by calculus too much, but I usually see this as a "find where the 'slope' of the curve crosses 0, so I usually add a couple of columns to compute some estimate of the slope at each point. Because of signal noise, there will usually be some question of how much "smoothing" to apply to the signal in estimating the slope.
2) Once the reference point is located and the time value for that point obtained, getting both curves on the same time scale should be a simple subtraction. I will usually add a column or two to subtract each time value from t for each curve, so that each curve/peak starts at time t=0. It is certainly not the only way.
3) Once these "helper columns" have been calculated, plot the data, using these helper columns for the x values.

[talkative__]

Thank you for your reply. to be honest i'm a beginner in excel is it possible to explain clearly how can I do it in excel?

[MrShorty]

As a beginner in Excel, what can I assume you know how to do? The graph pictured in the first post is a decent looking Excel graph, can I assume that you will be able to generate the "synchronized" graph once we figure out steps (1) and (2)?

Step 2 should be fairly straight forward. Put the "reference" time for each data series in a cell, then, with the right combination of relative and absolute references, it should be easy to put, in column F for example, =A2-$F$1 (A2 has the time data, F1 has the reference time value), then copy that formula down. Are you familiar with building these kind of simple formulas in Excel?

As I said, step 1 is probably the hard part of this whole thing. If you do not require complete automation, I would probably just manually pick out the reference time and enter it into a cell like F1.

Beyond that, I think if you want specific help, we will need you to put together a spreadsheet with what you know how to do. Explain to us what you can do, what you cannot do, what you need the spreadsheet to do and what you can expect your users to be able to do. It will then be a lot easier for us to provide specific help and suggestions.