how to add and subtract Global variable's value for approval points through scripting?

[LadyOfFrost]

New to modding (and specifically scripting!) and I'm currently trying to make a follower mod. I'd like to have approval/disapproval points using global variables, but I don't know how to add and subtract the value only how to set it to a specific value. What I'd like is 0-100 value and then certain choices would add or subtract points to the value.

 

So for example if my GlobalVariable ID is Follower_Approval and I want it to add 5 to the already existing value, how would I go about this? Or is there another way to make an approval system work in an easier way?

[scorrp10]

For Global, if in a script you have

GlobalVariable Property Follower_Approval Auto
Float Points  = 5.0

and it is filled with proper FormID in the script properties

One option is:
Follower_Approval.SetValue(Follower_Approval.GetValue() +  Points)

Not sure if this function is SKSE - and how old - but you can also:
Follower_Approval.Mod(Points)

I have seen a number of ways of handling such things.

Set up a faction, add player to it, and value is player's rank in that faction.

Set up a chest in some inaccessible location, and add stuff to it.  Item counts represent values. 

[LadyOfFrost]

Thank you very much Scorrp10 for the help!