PPI Guru is utility to calculate display's PPI (Pixels Per Inch) of Phones, Pads or Laptops, even Monitors.
For calculating PPI of specified display, just input screen width, height in pixels and diagonal size of the screen in inches, the PPI will be auto calculated and show in result. And it will indicate that display is or not a Retina Display. (Retina Display means (size greater or equal than 10″ and PPI greater or equal than 200) or (size less than 10″ and PPI greater or equal than 300)).

Key Features:
• Calculating PPI automatic
• Search device information from internet
• Retina Display indicator
• Save device information

For public sale devices, you can just enter device name, then press Search Info, PPI Guru will search that name with Google, then grab display's information of that device.
PS. Search Info may not return accurate information, and it depends on accessibility to Google.
Device's information could be saved in local database for further reference.