This Type H calculator is one of the rarer models in the Fowler's circular slide rule range and represents one of the earliest double sided designs introduced by the company during the first quarter of the 20th century.

Dating to around 1920, the Type H followed the Scientific Publishing Co. Fowler's Patent Pocket Calculator, which was patented in 1910. Measuring 2⅝" (68 mm) in diameter, excluding the stem and thumb ring, the serial number '4040' is etched onto the side of the frame.

The card scales are both clean and legible, rotating smoothly in both directions direction upon turning of scale and cursor knobs and sit beneath a clear glass which is from free of any chips or damage.

The calculator is accompanied by its original leather case, bearing the inscription 'With the compliments of HOMATRA LIMITED British Oil Burning Systems' in gold lettering on the flap (see photos), indicating they were given as a client appreciation gift.