I am working in the interface for a software, and it is very important to keep it as simple as possible. For this specific problem it was decided that colours should be avoided (if possible), so not to cause problems for people with colour-blindness.
The information that I need to display is a performance metric in a certain time interval compared to the performance for a previous time interval - for that an arrow is used: pointing up means improvement, pointing down means decline, pointing to the right side means "no significant change". However another metric needs to be displayed: a goal for the performance - the best solution I could come up for that was a horizontal bar: if the arrow is below the bar it means we're below the goal, if the arrow is above the bar, it means we are above the goal, and if both are at the same level, it means we're very near the goal.
This is an example mockup I made:
The problem with this solution is that it is very easy to confuse the meaning of the vertical position of the bar: the bar being at the top actually means "bad". Compare cases 2 and 6 on the mockup.
What could I do to improve this interface? I believe it is a simple and elegant solution, I just need a way to remove the ambiguity cited above.