Old calculators existed, but they had three fatal flaws:
Additionally, the current flowing out of Pin 7 determines the brightness of the LEDs. The LED current ( ILEDcap I sub cap L cap E cap D end-sub ) is approximately 10 times the current through lm3915 calculator updated
This is where most people get confused. R2 sets the "floor" or the specific range voltage. Old calculators existed, but they had three fatal