Here are photos of two Produx Original calculators. Both have green/clear vinyl slip cases and metal tipped, black plastic handled, styli. I also have the instructions from both - these cover both numerical and sterling calculators so I have two identical copies. Both calculators are 6.5" x 3.4". They were made in West Germany, probably in the 1960s. They are virtually identical except that one is sterling and the other is decimal.

Source: David Riches's Collection

X-Number World of Calculators