The very rare Tektronix 31 presented here is a very powerful calculator for its era but unlike the HP-9100 it never managed to acquire a significant share of the market. Perhaps that is why it is quite rare.
The device presented here is a 220V device. Its power source has been refurbished (new capacitors) and its display has also been refurbished. The calculator works well in standard “calculator” mode.
The service manual is also present with the machine.