On page 179 of the first volume of the Journal, Commander J. Middendorp, R.N.N.R., discusses the effect on the observed altitude that arises when the sextant is tilted out of the vertical plane, and concludes that the error is a maximum for altitudes in the region of 45; it seems to me that the conclusion is incorrect. I have no quarrel with Commander Middendorp's mathematics, but with his fundamental hypothesis, which is that when a sextant is tilted it is rotated about the line of sight to the star. I believe on the contrary that a sextant tilt is a rotation approximately around a horizontal axis.