def removeStartTime(sortedData):
    """Removes start time from time values

    Arguments:
        sortedData {list} -- the data sorted with lowest time first
    """
    t0 = sortedData[0][0]
    for i in range(len(sortedData)):
        sortedData[i][0] = sortedData[i][0] - t0
        sortedData[i][1] = sortedData[i][1] - t0
    return sortedData