A thickness meter of magnetic type for measuring the thickness of non-magnetic film plated on magnetic base is constructed.
The essential part of this meter is "magnetic needle". This is made of iron having high magnetic permeability and is constructed so as to put one end of this needle vertically on the film to be measureb (non-magnetic and plated on mlagnetic base) and is magnetized and attracted upward by a coil placed at the other end of the needle.
In the case of measurement, the needle, after putting on the film, is magnetized gradually by increasing the current of the coil. Then, at a point, the needle is suddenly separated from the film and jumps up. From the burrent at this point, the thickness is determined.
Though the magnetic property and surface condition have a certain effect on the sensibility of the meter, it was possible to measure the thickness in the range from 0.002mm up to 0.5mm within the error of naerly±10%. This meter can be used as a rapid and non-destructive tester at laboratory and at factory.

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The author had described the method of evaluation for the dynamic behaviour of indicating instruments in the first three sections of Part III. (Keisoku Vol. 5, No. 2). This paper, the latter sections of Part III, also relates to a method for assessing the performance of indicating instruments. As a criterion for this it is possible to use the error area A0 which is represented by following equation and Fig. 4,
where Y₀(jω) is the frequency characteristics of indicating instruments and Y_s(jω) is the frequency characteristic of a idealized system which gives quickest response without overshooting shown in Fig. 2. The author points out that the Y_s(jω) is composed by the ideal filter shown in Fig. 1 and cosine squared filter as shown in Fig. 3.
The results of evaluation for typical measuring systems are shown in Figs. 5, 6, 7 and 8. And it is assumed that the measuring systems which give quickest response without overshooting generally have maximally flat phase characteristics ψ(jω). Figs. 11, 12, 13 and 14 show the dψ(jω)/dω and it is used for assessing the degree of this flatness.

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The theory of U tube manometer is developed using the results of hydrodynamical calculations of oscillatory flow of the manometer liquid. Natural frequencies and amplitudes of forced oscillation was calculated with satisfactory agreement with experiments. The experiments were consecuted with three kinds of liquid, water, ethyl alcohol and mercury. The manometer tube size is diameter: 3.48 5.00 8.92mm length: 30 50 70 100cm The effect of surface tension was also considered with certain assumption of meniscus formation. The surface tension has the character of Coulomb-like friction and considerable effect on the maximum amplitude of resonance curves and the damping constants of free oscillation.

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