I’ve had this problem too. When you’re in the field, all of these smart phone devices are hard to see. Tablets are worse! Getting an iPad pushed me over the edge on this one. As of version 2.1 (now available on Android and should be on iOS next week), you can switch the display to “Daylight Display Mode” by (1) pressing and holding the ⓘ symbol (in the top left corner) and then tapping on the [+] key. BuildCalc will go from a display as shown on the left to that on the right … which looks great in full sun.
Repeat the above steps to turn off “Daylight Display Mode”. Also, you can switch “Daylight Display Mode” by going to BuildCalc’s preferences via [Conv] [Prefs].