Dump trucks
A slide rule for every occasion.
Do you ever get the feeling that these days there's an app for everything?
I think people used to feel that way with slide rules. For example, there used to be a slide rule for feeding pigs. Nowadays, it is replaced by an Android app: SwineApp.
When I was searching through old editions of "De Ingenieur", that feeling struck me again.
In "De Ingenieur" of 10 March 1939, a French slide rule is discussed for calculating garbage collection rides in Paris.
Figure 1: French dump truck slide rule
It works very simple: set the 0 of slide A opposite the length of the street. Put the number of garbage cans on slide B opposite the number of stops on the corresponding scale. Under an arrow of B on slide A, read the duration of the garbage collection. There are two arrows: a red and a black one corresponding to a red and a black scale A. There are two drawbacks: a cursor is missing, and the ruler is specially made for S.I.T.A. garbage trucks with two garbage collectors.
I haven't found an Android app that does exactly the same thing yet, but DumpTruckMath comes pretty close.
Figure 2: a S.I.T.A. dump truck near the Notre Dame
Figure 3: with so many dump trucks, you do need a slide rule.
UPDATE:
In the UK, another dump truck slide rule was developed in 1928, see Paul J. Crowther, "What a load of Rubbish", Skid Stick 18, September 2004, page 8