This paper analyzes the accuracy of multigrid truncation error estimates, examining how m depends on the grid transfers employed. In particular, we compare two definitions of the relative local truncation error (a computable estimate of the truncation error difference between two grids) found in the literature. One definition requires a careful choice of high-order grid transfers to achieve accurate estimates (e.g., Bernert, 1997), while the other (e.g., Schaffer, 1984) can utilize simpler grid transfers (and is itself simpler to compute). Our analytical results are illustrated with numerical calculations for several model problems.