I just wrote a simple patch which adds minimal and maximal voltage to display. I find it very useful when debugging R2R D2A, so if you think it's useful feel free to include it in next version of OpenHantek.

It's available at https://github.com/dpavlin/openhantek/commit/4d75699670b5bb61dc77c37c70b7a1fd29fca14f

Thanks for OpenHantek, and keep up the good work! It's very useful tool in my toolbox.