A more recent development is the indeterminate progress bar, which is used in situations where the extent of the task is unknown or the progress of the task cannot be determined in a way that could be expressed as a percentage. This bar uses motion or some other indicator to show that progress is taking place, rather than using the size of the filled portion to show the total amount of progress, making it more like a throbber than a progress bar (see also barber's pole). There are also indeterminate progress indicators, which are not bar shaped.