http://pmo5e085f.pic23.websiteonline.cn/upload/api_610_10th_...According to this API document about, "Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries", page 49 states
"All bearing housings shall be dimpled at the locations shown on Figures 27 and 28 to facilitate consistent vibration measurements. The dimples shall be suitable for accurate location of a hand-held vibration transducer with an extension “wand”. Dimples shall be either cast or machined and shall be nominally 2 mm (0,080 in) deep with an included angle of 120°."
Pages 40 and 41 have diagrams of the dimples and also for the optional arrangement for mounting vibration-measuring equipment