Slide rule for reading data on bingo grid - has plastics sleeve with windows containing slide with erasable data

摘要

The reading aid is for grids containing data, especially for games of chance such as lotto. The data is read off by a slide rule along the card. The card is inserted into a support. A transparent plastic traveller with windows enables the figures on it to coincide with the figures on the card. Figures written in erasable ink are employed.