Western Union developed Teledeltos paper in the late 1940s (several decades after it was already in use for mathematical modelling) for use in spark printer based fax machines and chart recorders.
[2][3] Each painted area has a sufficiently low resistivity (relative to the carbon) and to be assumed to be a constant voltage.
Stanley Hooker describes its use pre-war, although he also notes that compressibility effects could be modelled in this way, by sculpting the base of the tank to give additional depth and thus conductivity locally.
If the external airflow is restricted, the 'ambient' electrode may be subdivided and each section connected to a common voltage supply through a resistor or current limiter, representing the proportionate or maximum heat flow capacity of that airstream.
This has been performed, in a manner analogous to Teledeltos paper, by using volume tanks of a conductive electrolyte.
[6] This thermal modelling technique is useful in many branches of mechanical engineering such as heatsink or radiator design and die casting.
[7] The development of computational modelling and finite element analysis has reduced the use of Teledeltos, such that the technique is now obscure and the materials can be hard to obtain.
[2] Its use is still highly valuable in teaching, as the technique gives a very obvious method for measuring fields and offers immediate feedback as the shape of an experimental setup is changed, encouraging a more fundamental understanding.
[3][4] Teledeltos can also be used to make sensors, either directly as an embedded resistive element or indirectly, as part of their design process.
Its resistance is slightly sensitive to applied mechanical strain by bending or compression, but the paper substrate is not robust enough to make a reliable sensor for long-term use.