Bruel & Kjaer - 2511 documentation, here :

http://ims.si/documents/2511_product_data.pdf

http://www.helmut-singer.de/pdf/b+k2511.pdf

https://www.bksv.com/media/doc/bb0694.pdf

http://meteosat.pessac.free.fr/IMA/ressources/tp_avio/TP_Vibration/DocTP_vibration_avionique.pdf

Applications :

https://www.bksv.com/media/doc/17-227.pdf

http://inpressco.com/wp-content/uploads/2013/08/Paper27892-896.pdf

https://www.researchgate.net/profile/Arturas_Kilikevicius2/publication/251315132_Comparison_of_the_Comparator_Carriage_Vibration_Velocity_Measurement_Methods/links/54462e540cf2d62c304da9f1/Comparison-of-the-Comparator-Carriage-Vibration-Velocity-Measurement-Methods.pdf