I use Arduino uno and QTR 8RC sensor array. also I try code that published “https://www.pololu.com/docs/0J19” under arduino library. However I dont want to calibrate QTR 8RC for all I give power to my line follower robo. because there is no change with the black and white line in my project. IS there a way that qtr remember last black line calibration?? 
Hello.
You can write the calibration values to your Arduino’s EEPROM to store them for when the Arduino is powered down. You can see how to do this in this EEPROM Write tutorial. When you power up the Arduino again you can read the values back from the EEPROM. You can see how to do this in this EEPROM Read tutorial.
Please note that your stored calibration values might not be the best settings for all lighting conditions.
-Derrill
Thanks a lot
We have both QTR8RA and QTR8RC sensor arrays. Although we have faced no problem for QTR8RA (calibration values can be stored and used in a different code written by us in an additional file) applying the code given in Pololu library for calibration, for our QTR8RC sensor array, we could not use calibrated values in our seperate code file . We have to make calibration at the beginning of our code each time. What is the way to store the calibrated values and use them afterwards in a different code file? Thanks for your consideration.
Can you post the code you are having problems with?
-Derrill