Complex sentence: The Zoroastrian religious calendar, which is still in use today, uses the regnal year of Yazdegerd III as its base year, and its calendar era (year numbering system) is accompanied by a Y.Z. suffix.
Split into simpler sentences: The Zoroastrian religious calendar, which is still in use today, uses the regnal year of Yazdegerd III as its base year. Its calendar era (year numbering system), which is accompanied by a Y.Z. suffix.