Abstract: Simple rhombus and duplex rhombus are the best figures for base expassion. Investigations on the strength of such kind of base-nets are generally made on the assumption that the figure has the form of a normal rhombus, i.e. the sides of the quadrilater al are equal in length. But in practice, it is impossible to lay out such rigoious figrres in field. In this paper the author investigates the effect of deviations from a normal rhombus on the reciprocal of the weight of the expanded side. The main conclusions drawn in this paper are following; (1) It is desirable to make the two sections of the expanded side, divided by the base, nearly equal to each other, the ratio of their lengths preferably not more than 2, nor less than 1/2. (2) The angle of interseotion of the expanded side with the base may differ from a right angle by as. far as 30° without causing serious effect on the reciprocal of the weight of the expanded side. (3) It is not preferable to use a triangle with interior station as base-net. Besides, the author suggests some simple formulae for estimating the reciprocal of the weight of the expanded side, which are convenient for use in field."