position = [
['2019-05-01', '- 6'],
['2019-05-02', '+5'],
['2019-05-03', ' 5'],
['2019-05-04', '4'],
['2019-05-05', '5'],
['2019-05-06', '5'],
['2019-05-07', '4'],
['2019-05-08', 'Error 5'],
['2019-05-09', '3'],
['2019-05-10', '3'],
]
count_lines = 0
total_position = 0
wrong_lines = 0

for row in position:
    try:
        count_lines += 1
        level = int(row[1])
        total_position += level
        print(total_position / count_lines)
    except:
        wrong_lines != int(row[1])
        print('Количество измерений', count_lines)
        print('Количество некорректных строк', wrong_lines)