Years

P1

P2

P3

P4

Total

Length of phases

Base years

1961-1990

15

40

32

50

136

periods

2000-2030

13

38

32

48

130

2030-2050

10

36

31

45

122

Changes in length

2000-2030

−2

−2

0

−2

−6

of phases

2030-2050

−5

−3

−1

−5

−14