How much was a bit in the Old West?

I'm curious to know, in the context of the Old West, what was the value of a "bit"? Was it a standardized unit of currency, or did its worth vary depending on location, time period, or other factors? And if so, how did one go about determining the value of a bit in a given situation? It's fascinating to think about the economic systems and currency used in the Old West, and I'd love to gain a better understanding of how a bit fit into that landscape.