The problem is often that the directional indicators are not in a readable place. Often you have to have a light shining on them, but they are in a cavity in t

The problem is often that the directional indicators are not in a readable place. Often you have to have a light shining on them, but they are in a cavity in the device that you can't look into and easily shine light into at the same time. This is what I meant by "at an angle that it's hard to shine light on them and look into the device at the same time", in case it was ambiguous. But I really think having them keyed is the way to go. You can put cylindrical batteries in either way, and that's the problem. You can't even reliably attach a 9-volt the wrong way, and often times the 9-volt battery compartment won't close unless the contacts are fully attached.