Ok slide rules etc.. straight ones, and round ones too! analogue computing devices.
They are quick, efficint and don't need any batteries.
Below is a British Thornton AD150. A general purpose sliderule.
Below, a rather specialized Fisher GEC Elliot mark VIE used for valve sizing etc..
Below, an ex-ministry "Computer Dead Reckoning MK4A".
(Referance No 6B/2645) Size is about 6 inches Diameter.
Below, an ex-ministry "Height and True Airspeed Computer MK4".
(Referance No 6B/345) Size is about 6 inches Diameter.