I want to calculate the value percentage in the following scenario:
I have some values obtained using X method and some others obtained using Y method.
The values obtained from X are: 2.5, 1.14, 21.96, 4.66, 1.91, 735.93, 30.96
The values obtained from Y are: 2.5, 1.11, 21.19, 4.63, 1.89, 710.24, 31.02
The values obtained using X are within ...-...% of those obtained in Y.
How do I calculate the percentage on the above statement?
Typically you would decide on one of $X,Y$ as the standard to measure from and measure the error of the other from that. If you choose $X$ as the standard for the $i^{th}$ value the error in the calculation of $Y_i$ is $\left|\frac{Y_i-X_i}{X_i}\right|$. You would calculate all of these and report the maximum or maybe round it up to a nice value. If the errors are small it won't matter much whether you use $X_i$ or $Y_i$ in the denominator. If they are large it will matter and you should make it precise.