In his attempt to improve the 1954 calibration tables for the various plunger loads of the Schiøtz tonometer, Friedenwald's major consideration was that such attempt should least disturb the calibration of the 5.5 gm. plunger load. His decision was greatly influenced by the agreement between the estimate of the mean intraocular pressure obtained by Goldmann with the use of his applanation tonometer (14-15 mm. Hg) and that determined independently at the Wilmer institute with the use of the 5.5 gm. plunger load of the Schiøtz tonometer and the conversion tables of 1954 (15-16 mm. Hg).4 This agreement was considered excellent in the light of the findings of Linner9,10 "that the episcleral venous pressure rises 1 mm. Hg when the subject changes from the erect to the recumbent posture"4 as is the case in Schiøtz tonometry.
Friedenwald, however, pointed out that further check on this agreement had to
ARMALY MF. Schiötz Tonometer Calibration and Applanation Tonometry. Arch Ophthalmol. 1960;64(3):426–432. doi:10.1001/archopht.1960.01840010428016