def clause_15_6_6_e_merging_flow_1(N: float, X: float, D: float, S_up:
    float, W_SE: float) ->tuple:
    """Calculates merging flow at final exit level in accordance with Figure 6 (1 of 3) in BD 9999:2017, page 68.
    Merging flow from stair with storey exit at final exit level.
    SI UNITS unless specified.

    :param N: is the number of people served by the final exit level storey exit.
    :param D: is the lesser distance from the final exit level storey exit or the lowest riser from the upward portion of the stair, in metres (m).
    :param S_up: is the stair width for the upward portion of the stair, in millimetres.
    :param W_SE: is the width of the final exit level storey exit, in millimetres.
    :param X: is the minimum door width per person (see 16.6 and Clause 18), in millimetres.
    :return W_FE: is the width of the final exit, in millimetres.
    """
    S_up *= 1000.0
    W_SE *= 1000.0
    X *= 1000.0
    condition_check = False
    if N > 60 and D < 2:
        condition_check = True
        W_FE = S_up + W_SE
    else:
        W_FE = N * X + 0.75 * S_up
    W_FE = max([W_FE, S_up])
    W_FE /= 1000.0
    return W_FE, condition_check
