As plastics were increasingly used to manufacture calculators, manufacturers competed to develop lighter and more compact products. The double injection method was used to imprint black letters and numbers on the white surface of the key pad. The LC-78 calculator had 5 or 6 components and keys all printed on a surface the size of a business card. Casio's SL-800 was 0.8mm, as thin as a credit card, and weighed only 12 grams.
(Photos, upper: LC-78 Bottom: SL-800)