victorfb:
that was what I needed thank you. but now how can I use the values that I stored on the file, I was able to read the files back from the file and now I need to use these values. can I go backwards and read these values 3 by 3 as I was reading from the sensors?
I'm sure the answer is yes, even though I have not progressed far enough myself to be sure I understand the question - particularly the last sentence.
Essentially: no matter what you want to do, if you can see it sensibly, you can use it sensibly. Even if you can't see it sensibly, i.e. just a continuous stream of numbers, it is still possible to use it sensibly but it involves a lot of work you would probably rather not know about.
Sticking with the first, by seeing sensibly, I mean easily understood on the monitor. A properly formed CSV file is formed the same way as a properly formed display on the screen. It can even be exactly the same, whereby the file is derived from the monitor.
So the code in the loop looks like
Serial.print(var1);
myFile.print(var1);
Serial.print(" , ");
myFile.print(" , ");
Serial.print(var2);
myFile.print(var2);
Serial.print(" , ");
myFile.print(" , ");
Serial.print(var3);
myFile.print(var3;
Serial.println(" , ");
myFile.println(" , ");
which gives three columns, one row for each loop. The println at the end is the vital punctuation. You don't actually need the commas in the serial stuff, just the spacing. The commas don't get printed on a spread sheet. They are just signals.
I'm not sure this helps, principally because I'm not sure what you want to do. I'm a newbie too and, at the moment, II don't use the SD to disseminate data, it is just a backup.