I had an old solar powered version of TI-30 calculator that I purchased maybe around 1998 or 2000, which I liked and was accustomed to using. Finally a couple months ago a few of the buttons near the bottom, the decimal point and zero mainly, started to get unreliable. My work as an R&D machinist cutting into costly one-off prototype parts requires me to avoid errors as much as possible, so I bought a new battery-only TI-30Xa as a replacement. Well that is OK but it powers down pretty soon if left for a few minutes. I often like to refer back to my last result to remind/reassure myself that I have not had a brain fart, and my old solar one would stay on indefinitely as long as the lights were on.