What does RMS stand for? A physics application I'm using reports for a first order fit of the three points below as $11.388612x - 301.878$.
   x, y    
  35, 0
  430, 4861
  656, 7000

It also shows a field labeled: "RMS: 329.499"  
How is that RMS calculated? I tried  RMSD as defined here but didn't get the same value.
 A: RMS stands for the root mean square error. It's calculated in the following way.


*

*First we calculate the residuals: -96.72, 265.77, -169.05

*Next we calculate the squared residuals: -96.72$^2$,  265.77$^2$, -169.05$^2$

*Then we sum and divide by $n-2=1$

*Take the square root.



Further info
A residual is simply the $observed - fitted$. So when x = 35, the observed is 0 and the fitted value is 
\begin{equation}
11.388612\times 35 - 301.878 = 96.72
\end{equation}
The residual is then: $0 - 96.72 = -96.72$
A: That's the root mean square error (RMSE) of the regression.
$$RMSE = \sqrt{\frac{1}{n-k}\sum{(y_i-\hat{y_i})^2}},$$
where $y_i$ is the observed and $\hat{y_i}$ the fitted value for observation $i$, $n$ is the number of observations, and $k$ is the number of parameters fitted (including the constant).
I just tried fitting a straight line by simple linear regression in another statistics package and got an RMSE of 329.499751.
A: It's the RMS (root mean square) of the residuals of the linear regression.
In R:
> x <-c(35, 430, 656)
> y <- c(0, 4861, 7000)
> mod <- lm(y~x)
> mod

Call:
lm(formula = y ~ x)

Coefficients:
(Intercept)            x  
    -301.88        11.39  

> sqrt(sum(resid(mod)^2))
[1] 329.4998

