Grappendorf.net showcases a modular analog computer kit:
Inspired by Dr. Vogels Home Brew Analog Computer, this kit consists of various 100×60 cm PCB cards which can be connected together with 2.54 mm jumpers. Each board implements a specific section of the analog computer by Dr. Vogel. Connect the various input and outputs of generators, adders, integrators and multipliers to compute different mathematical functions.
This kind of electronic computation was used for real applications in the years 1950 to 1970. You could use them to solve quite complicated differential equations and display the solution with on an oscilloscope. Two of their main disadvantages were bad calculation accuracy (due to the tolerances in non-linearities of the electronic components) and a limited value range (e.g. due to clipping of the op-amps).
Some simple example calculations implemented with the modules below:
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