Okay, ding ding, my turn...

I love analog and shoot LF as my hobby. On the week days I help people find solutions to problems requiring high-speed dig&#^l cameras. This week I had a situation where I needed x2 TSE lenses but unfortunately Nikon have removed the aperture lever fom their latest model macro, meaning we can't stop down with our camera mount. We've gone for the Schneider option, but I had to do a myriad of calculations to see if at the swing we required and the min focus distance, I'd get enough DOF. I needed some calculations to pre-visualize. Can't do that on a ground glass.

Point is, think outside the box. An iPhone app could have saved me literally an hour or more of time.
My eyes aren't great either so with macro on LF, I'd love an app. Technical photography is part visual with a whole lot of mathematics...take a peek at the ground glass, but also take out the calculator guys!