The invention of the integrated circuit in the late 1950's led to first 4 bits generation of microprocessors/controllers in the early 70's. While the Intel 4004 was the first commercial microprocessor, the TMS 1000 for Texas Instruments was the first widely available microcontroller embedding CPU, RAM and ROM for a mere 2$. Millions of units of this family were deployed in many calculators and handheld games. This talk will have a retrospective look at this piece of history based on an Harvard architecture. We will first analyse the die, especially how to visually decode its rom content and disassemble it. Then we will have a look at its instruction set and look at the coding of some basic operations found in early calculators, including "reversed" calculators such as the famous little professor and other handheld games of this time. We will show this in action using the Mame emulator and have a look at how Mame handles the TMS 1000 (including some specific display or input controls, e.g. Merlin). Last but not last, you will discover and be able to play with our Big Professor A3 version based on an Arduino Nano, LED matrix and 3D printing!