Coal mining using a motorised coal breaker.
These stamps were engraved by Czesław Słania.
Plan 6-letni to 100 000 000 ton wegia w r(oku) 1955 = The Six-Years Plan means a hundred million tons of coal in the year 1955.
Poland - Economic development (www.nationsencyclopedia.com)
Poland establishing the planning formula (www.photius.com)
FDC Fischer 577-578