Complex sentence: By the end of the 19th century, when better copying methods had become available, the copying pencil was being used only as an indelible pencil, a precursor to the ball-point pen.
Split into simpler sentences: By the end of the 19th century, better copying methods had become available. Consequently, the copying pencil was being used as an indelible pencil, a precursor to the ball-point pen.