A ruler at hand.
With this app you can measure small objects or up to one meter, sliding the ruler.
You can also take the measurements in cm, mm and inch, and set the ruler is in centimeters or inches.
It is recommended to measure the display of your device and enter the actual measurement, it is also possible to automatically detect the size of the display.
To activate the options and hold on the "Settings" at the bottom right. For other options, press the "Options" button on your device.