 Mechanical type systems introduced near the end of the 19th century , such as the <unk> and <unk> machines , allowed for some variable sentence spacing similar to hand composition . Just as these machines revolutionized the mass production of text , the advent of the typewriter around the same time revolutionized the creation of personal and business documents . But the typewriters ' mechanical limitations did not allow variable spacing — typists could only choose the number of times they pressed the space bar . <unk> in some English @-@ speaking countries initially learned to insert three spaces between sentences to approximate the wider sentence spacing used in traditional printing , but later settled on two spaces , a practice that continued throughout the 20th century . This became known as English spacing , and marked a divergence from French typists , who continued to use French spacing . 
