x = x * 26 + c as u64 - 'a' as u64 + 1;
          if x > Self::SUPPLY {
            bail!("sat name out of range");
          }
        }
        _ => bail!("invalid character in sat name: {c}"),
      }
    }
    Ok(Sat(Self::SUPPLY - x))
  }

  fn from_degree(degree: &str) -> Result<Self> {
    let (cycle_number, rest) = degree
      .split_once('°')
      .ok_or_else(|| anyhow!("missing degree symbol"))?;
    let cycle_number = cycle_number.parse::<u32>()?;

    let (epoch_offset, rest) = rest
      .split_once('′')
      .ok_or_else(|| anyhow!("missing minute symbol"))?;
    let epoch_offset = epoch_offset.parse::<u32>()?;
    if epoch_offset >= SUBSIDY_HALVING_INTERVAL {
      bail!("invalid epoch offset");
    }

    let (period_offset, rest) = rest
      .split_once('″')
      .ok_or_else(|| anyhow!("missing second symbol"))?;
    let period_offset = period_offset.parse::<u32>()?;
    if period_offset >= DIFFCHANGE_INTERVAL {
      bail!("invalid period offset");
    }

    let cycle_start_epoch = cycle_number * CYCLE_EPOCHS;