This minimal and maximal values can be changed using the Progressbar.range property.
Progressbar.position read/write property
Get or set the Progressbar current progression position. The position start from 0 and increase to the maximal position (defaulting to 100).
Example
local ui = require "ui"
-- create a simple window
local win = ui.Window("Progressbar.position sample", 320, 200)
local pb = ui.Progressbar(win)
win:status("")
pb:center()
win:show()
-- update user interface and increase Progressbar progression
repeat
pb:advance(1)
win:status("Position = ".. pb.position)
ui.update()
until pb.position == 100