Ruler app designed for objects and maps measurement with various scales selectable. Both units system available: metric (meters) and imperial (Inches, feet and statue miles).
It's perfect tool for engineers, modelers, designers and many more.

Became beta tester for new version:
https://play.google.com/apps/testing/com.pawel.easyscaleruler

Features:
-NEW in 2.1: calibration using credit card as length reference
-Possibility to define your own scales and store them in phone.
-over 30 predefined scales
-measuring in 2 units systems
-protractor mode for angles measurement
-on screen touch marker for precise measurement
-energy saving mode for OLED screens

Energy saving (night) mode. Designed mainly for smartphones with OLED screen (saves over 50% energy).

It's possible to measure scaled models to check the corresponding dimensions against the original.
Precise distance measurement by dragging green marker and angles measurement by protractor.

It's also possible to measure distance on map in scale (in miles or kilometers).

Calibration procedure:
1. Open ruler in 1:1 scale
2. Click "Calibrate" button and place credit card at screen
3. Drag blue line to match the edge of your card
4. Press OK to save settings or Cancel to exit calibration mode without saving.

Ruler app contains mainly scales for model trains:
*0 (both 1:45 - US and 1:48 - Europe)
*00 - British scale 1:76.2
*H0 - 1:87
*TT - 1:120
*N - 1:160
*Z - 1:220

There are also ruler scales used in other scale models (planes, ships kits etc.):
*1:18
*1:43
*1:72
*1:144

Map scales:
1:50 000
1:100 000
1:500 000 (ICAO - aviation)