Story point is a arbitrary measure used by Scrum teams. This is used to measure the effort required to implement a story.
In simple terms its a number that tells the team how hard the story is. Hard could be related to complexity, Unknowns and effort.
In most cases a story point range is
A fibonacci sequence is 1,2,3,5,8,13,21,34,45 . Teams use a modifier version of this which looks like 1,2,3,5,13,40,100. The reason Mike Cohn suggest this is because the original sequence suggests mathematical accuracy and real projects are not like that.
It is a relative term and does not directly co relate to actual hours . Since story points have no relevance to actual hours, it makes it easy for scrum teams to think abstract about the effort required to complete a story.
If you look at the Fibonacci curve it really takes a steep climb . If using this series consider not using 1 and 2.
Use 3, 5,8, 13, 40,100.
But how do you know which story is a 3 and which is a five. In order to do that each team would have to find a baseline story. It does not have to be the smallest one, but one that all in the team can relate too. From then on all sizing should be done compared to that baseline.
This also creates a lot of confusion as most scrum masters who come from a PMP background relate this immediately to hours.
Story points do not relate to hours. So lets just not compare them. There is another technique called ideal hours which can be used.
Story points creates lots of vagueness to your agile process. For every team, story size could mean different things depending on what baseline they chose. IF two teams are given exactly the same stories one can say their velocity is 46 and the other can say 14. Depends on what numbers they chose
So if you want to compare velocity between teams that’s a really bad idea as comparing velocity is like comparing apples and oranges. S o do not compare velocity across teams.
If you really have to track time then dont use story points at all,