now, the reason why noone cares to answer is the search bar in the upper right corner. Believe it or not, but I see this question almost on a weekly basis :S.
Now, I'm not saying asking is wrong... So additionally to the tip to search for "Health bar" , let's have a look at how to do it with just GUIs... Since I saw you already considered a mesh bar before.
A pivot is rather simple math. You see, you only see the final position/ rotation/ scale after each complete frame. That leaves you with plenty of time to do multiple transforms at once. So if your pivot point is supposed to be at the center of the bar, you'd first scale the bar, say for 10% in this example, which would be a normalized value (normalized means from 1 to 0) of 0.9. Then to make the pivot in the center of the bar, simply move the bar by half the amount of the scale on the same axis.
The actual FSM of this example would be like:
GLOBAL INPUT : Update
Start State
float operator
(
current stamina / max stamina = scale
)
float operator
(
scale / 2 = Xoffset
)
GUI texture
(
...
)
Now, each time something happens to your stamina, you'll have a send event action send the global event "Update" (or whatever) sent and update the position and scale of the bar.
If you don'w want the bar to be in the upper left corner, jsut add another float operator which adds a default value to your x-offset. For a smaller bar, divide the scale by another float value.
Hope this helps.