How this is calculated
The divisor is computed as round(Clock / (Oversample × Target Baud)) − 1, matching the common UBRR-style register formula used on AVR and many other UARTs. The actual baud rate is then back-calculated from that integer divisor, and the error is the percentage difference from your target. Keep error under about 2% for reliable communication — higher than that and framing errors become likely, especially at higher baud rates.