def dt_calc(etime):
    """Returns an interval of time that increased as the ellapsed time etime increases"""
    if etime <= 10:
        return 0.25
    elif etime <= 60:
        return 0.5
    elif etime <= 120:
        return 1.0
    elif etime <= 300:
        return 5.0
    elif etime <= 3600:
        return 10.0
    else:
        return 60.0