I have two continuous variables. Variable $X$ represents the true values (basically it is atmospheric pressure measured via a barometer). Variable $Y$ represents a way to approximate the atmospheric pressure based on altitude, temperature, and some other physical parameters. I have $n=17$ values.
The question now is, how close the approximations are to the true values, i.e., how close are $X$ and $Y$. It seems to me, that the Bland-Altman-Plot (as descriptive tool) and the Concordance Correlation Coefficient are appropriate to assess the agreement of the two variables and thus the accuracy of $Y$. My only concern is, that one of the variables represents the true value (i.e. $X$) and my understanding is, that the aforementioned methods apply to situations when I'm comparing two measurements without actually knowing the true values, i.e., inter-rater reliability.
My question is whether I can use those two methods and if there are other (more) appropriate methods.