The exact rate of exchange between st-ycrv and ycrv is determined by the market forces of supply and demand. As the demand for st-ycrv increases, the exchange rate between the two will increase as well, resulting in more ycrv for each st-ycrv. Additionally, the rate of exchange is also affected by compounding, which means that each st-ycrv you hold will increase in value over time, resulting in more ycrv for each st-ycrv. Ultimately, the rate of exchange between st-ycrv and ycrv is determined by a variety of factors, including market forces, compounding, and the overall supply and demand of each currency.