1. This is the first rule on my site from IWA. A company which is still in operation in Germany. Their method of making rules differs from the "traditional" method. The rules are made in three layers. The upper and lower layers are of clear plastic on which scales are printed. The middle layer consists of a spacer at the top and bottom. The thickness of the spacers is the same (or very slightly more) than the slide and the distance between spaces is the same (or very slightly more) than the width of the slide. The parts are both glued and riveted (the rivets can be seen in the detailed drawings below). The slide is made of opaque white plastic and also has scales on it. The company still produces, and presumably sells, a range of specialised rules including some like a body-mass index calculator for medical purposes. The company has a web site at: http://www.iwa-slidecharts.com/fr-main-E.htm
2. On the front the rule has a standard set of scales. The only slight differences from
a normal rule, apart from the method of construction, are:
- the presence of a log scale for Naperian logarithms (called Neper following
continental practice),
- a centimetre scale which also doubles as decibel scale,
- some extra gauge marks for the weight and resistivity of Copper and
Aluminium,
- the scales are labelled in a self-documenting manner with the function
rather than the usual letter, e.g.x2 rather than A,
- the x and x2 scales are also labelled P1: P2
and U1:U2/I1:I2 respectively.
3. On the back of the rule are the special scales for electronic calculations. One
interesting feature of the rule (see detailed images of the back of the rule) is that the
fixed scales are split into three sets. The first and third are in the "normal"
position at the top and bottom of the rule face but the second is between the other two
with scales from the slide visible above and below this scale. It enables relevant fixed
and moving scales to be placed side by side and would not be possible on a rule of
standard construction. The scales are:
- l wavelength.
- w angular frequency.
- f frequency
- C capacitance
- L inductance
