The Miyota caliber 5R21 is a super small quartz 2-hander watch movement with zero jewels. This caliber is made in Japan by the Miyota division of Citizen, LTD. Miyota states that the 5R21 is only recommended for use in lady’s size watches. This caliber is sometimes misspelled as SR21.
Miyota 5R21 VS 5R32:
There is a similar caliber 5R23 with the main differences being that the 5R21 discussed on this page is a 2-hand movement (hours and minutes only) VS the 5R32 which is a 3-hand movement (hours, minutes, seconds). This difference also means that the 5R21 is slightly taller at 1.9mm VS 2mm on the 5R32. Another notable difference is that the driving force needed for the seconds hand causes the 5R32 to have a 2 year battery life compared to the 5R21 with a 4 year expected battery life.
In official tech documentation, Miyota claims that the Cal. 5R21 has an average accuracy of +/- 20 seconds per month “under normal circumstances”.