These are the three variations of 21 jewel 2 Tone Crescent Streets. Movement Variation 2 (MV2) has the serial number next to the barrel bridge and 2 barrel bridge screws. MV3 has the serial number next to the barrel bridge and 3 barrel bridge screws. MV4 has the serial number on the barrel bridge. I believe these to be the production figures for each variation; MV2 1600, MV3 500 and MV4 1000.