LRV stands for Luminance Reflectance Value
TGSI stands for Tactile Ground Surface Indicator
The contrast formula used in the app for Australia is the Bowman-Sapolinski Equation with LRV readings which are to be obtained as noted in Part E3 or E5 of AS/NZ 1428.4.1-2009 and Part B4 of AS1428.1-2009 is 125(Y2-Y1) / (Y1+Y2+25) where Y2 is the LRV of the lighter area and Y1 is the LRV of the darker area.
The recommendations vary from 30% to 60% based on the element. Please refer to AS/NZ1428 suite of Australian Standards for details.
Note that LRV is on a scale of 0 to 100 (black to white), however both white and black are never absolute and therefore in reality B1/Y2 never equals 100 and B2/Y1 is always greater than 0.
Use app at your own risk. The app designer / Vista Access Architects shall not be held liable for use of the app.