APA (7th ed.) Citation

Hettwig, E. (1963). Direct distance dialing. Siemens.

Chicago Style (17th ed.) Citation

Hettwig, Emanuel. Direct Distance Dialing. Germany: Siemens, 1963.

MLA (8th ed.) Citation

Hettwig, Emanuel. Direct Distance Dialing. Siemens, 1963.

Warning: These citations may not always be 100% accurate.