Like the 2824, Cal. STP1-11 measures 11½ ligne (25.6 mm) in diameter. However, STP uses a longer, thinner mainspring allowing them to boost power reserve to 44 hours, six more than ETA. It is also equipped with 26 jewels, one more than the ETA. The extra jewel supports the top of the barrel arbor. Cal. STP1-11 is tested in 5 positions and are finished with côte de Genève.
Like the Valanvron VAL-24, the STP1-11 might be based on the Chinese Sea-Gull ST2130 ebauche. Both share the same architecture (nearly identical to the ETA 2824) and the photos on the STP web site include the label, “ST2100” under the movement. If this is the case, STP's finishing must add more than 50% value to the movement so it can legally be called Swiss Made.
The related STP3-13 movement adds a blued steel swan neck regulator to the basic STP1-11. The similar STP5-15 is an open heart version, while the STP6-15 is fully skeletonized. STP2-12 (including STP2-12-1, STP2-12-3, and STP2-12-6) have a power reserve indicator and added calendar complications.