Stryd calibration algorithm

stryd_calibration.py

import math

def calibrate_stryd(stryd_distance: float, real_distance: float,
                    current_calibration_factor: float = 100., 
                    max_deviation: float = 2., max_weight: float = 0.4444, verbose: bool = True):
    """Calculates the new Stryd calibration factor given a distance measured by Stryd vs in reality (in m).
    All calibration factors and the deviation are given with baseline 100 (as in Garmin watches).
    `max_weight` is in [0., 1.] and determines the maximum weight of the new data.
    
    Rules:
        1. Get the theoretical new calibration (straightforward).
        2. Weigh it with `real_distance` / 1000., but not more than `max_weight`.
        3. Calculate a weighted average of the current and new calibration.
        4. Round to the next decimal (Garmin only allows 1 decimal).
        5. Clip at 100. -/+ `max_deviation`.
    """
    calibration_adjustment      = real_distance / stryd_distance
    theoretical_new_calibration = current_calibration_factor * calibration_adjustment
    new_weight                  = min(real_distance / 1000., max_weight)
    weighted_average            = (1 - new_weight) * current_calibration_factor + new_weight * theoretical_new_calibration
    rounded_wavg                = math.floor(weighted_average * 10) / 10 if weighted_average > 100. else math.ceil(weighted_average * 10) / 10
    clipped_rounded_wavg        = min(max(100. - max_deviation, rounded_wavg), 100. + max_deviation)
    if verbose:
        print(f"Stryd is off by {(stryd_distance / real_distance - 1) * 100:.1f} % (+/-: too long/short)",
              f"Theoretical new calibration: {theoretical_new_calibration:.2f}",
              f"Weighting new data with {new_weight:.4f}",
              f"Weighted average: {weighted_average:.1f}",
              f"After rounding: {rounded_wavg:.1f}",
              f"After clipping: {clipped_rounded_wavg:.1f}",
              f"-" * 30,
              f"Set your new calibration factor to {clipped_rounded_wavg:.1f}",
              sep="\n")
    return clipped_rounded_wavg