A small doubt about slopes.

Question

In velocity vs time graph, the slope would be the acceleration. But if the slope doesn't exist ( the slope from the left doesn't equal the slope from the right ) what would the acceleration be? and what would be the ideal description for that movement?

by description

1. a=+ , v=+ the object is speeding up in the positive value
2. a=- , v=- the object is speeding up in the negative value
3. a=- , v=+ the object is speeding down in the positive value
4. a=+ , v=- the object is speeding down in the negative value
5. a=0 , v=+ the object is moving in constant speed in the positive value

6. a=0 , v=- the object is moving in constant speed in the negative value

7. a=? , v=+ ????????????????????????????????????

8. a=? , v=- ????????????????????????????????????

an example

t=4, t=7, t=23, t=25, t=27