pub fn rule_of_70(rate: f64) -> FinanceResult<f64>Expand description
Approximate years to double using the Rule of 70: 70 / (100 * rate).
§Errors
Same domain as rule_of_72.
§Examples
use finance_solution::{rule_of_70, FinanceError};
assert!((rule_of_70(0.08).unwrap() - 8.75).abs() < 1e-12); // 70/8
assert!(matches!(rule_of_70(0.0), Err(FinanceError::ZeroValue { .. })));