Is there a way to highlight the line that you are working on? or some other way to help keep track of the lines you already indexed?
You can turn on the ruler. Click on Data Entry, then click on Show Ruler. If you want to change the color or the transparency of the ruler, after you have activated it click on Batch, click on Settings. The downside of the ruler is that you can't change the size of the ruler. It adjusts automatically as you zoom in and out the image.
Hope that might help you.