Forrest M. Mims III, Understanding Digital Computers, Radio Shack, 1987
BCD TO SEVEN-SEGMENT DECODER LOGIC DIAGRAM
Take a close look at the readout of almost any digital watch, clock or pocket calculator, and you'll see the seven distinct segments of each digit position. Look closely and you'll also see the decimal point (calculators only).
Like the BCD-decimal decoder, the BCD to seven-segment decoder is a complicated logic network.
If you have a few spare minutes you can verify the operation of the BCD to seven-segment decoder with the help of the logic diagram and truth table, but it's really not necessary.