STP4-13 is an automatic watch movement with day and date wheels from Swiss Technology Production. It is based on Cal. STP1-11, itself a clone of the popular ETA 2824-2. STP uses a longer, thinner mainspring, boosting power reserve to 44 hours. It also includes an extra jewel on the barrel arbor.
The Day-Date STP4-13 uses an outer day wheel like the ETA 2834-2, increasing the diameter of the movement to 29.00 mm. Cal. STP4-13 was first introduced in 2017 and remains in production today.
STP may have used an ebauche from Sea-Gull in China to build the STP1-11 family. Photos on the company web site previously included the label, “ST2100”, which is the identifier found on the Sea-Gull ST2130 movement. The same has been said of the Valanvron VAL-24. Due to their Swiss content and finishing, STP can legally classify these movements as “Swiss Made”, and the company may now construct most or all of the movement in-house.
The movement can be manually wound with the crown in position 1. Rotate the crown clockwise to wind the mainspring.
The day and date wheels are advanced with the crown in second position (one notch out). Turn the crown counter-clockwise to advance the date wheel by one day. Turn the crown clockwise to advance the day wheel.
The time is set with the crown in third position (pulled all the way out). Rotate the crown clockwise to advance the minute and hour hands and counter-clockwise to turn them backward.