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Operating, Testing, and Preventive Maintenance of Electrical Power Apparatus: Hubert, Charles I.: 9780130417749: Amazon.com: Books
![Dr. Hubert Frings operates a tape recorder while his wife, Mable, holds a microphone to record insect calls, - Penn State University Archives Photograph Collection - Penn State University Libraries' Digital Collections Dr. Hubert Frings operates a tape recorder while his wife, Mable, holds a microphone to record insect calls, - Penn State University Archives Photograph Collection - Penn State University Libraries' Digital Collections](https://digital.libraries.psu.edu/digital/api/singleitem/image/psuphoto/187/default.jpg)
Dr. Hubert Frings operates a tape recorder while his wife, Mable, holds a microphone to record insect calls, - Penn State University Archives Photograph Collection - Penn State University Libraries' Digital Collections
![Operating, Testing, and Preventive Maintenance of Electrical Power Apparatus: Hubert, Charles I.: 9780130417749: Amazon.com: Books Operating, Testing, and Preventive Maintenance of Electrical Power Apparatus: Hubert, Charles I.: 9780130417749: Amazon.com: Books](https://m.media-amazon.com/images/I/51R807N3TJL._AC_UF700,800_QL80_.jpg)