How to use it
Sign in with a free account, choose your colour and where your home board is, then upload a photo of the board: a picture of a real board taken from above, or a screenshot of an online one. Keep the whole board in view, every checker visible and the dice showing. The board is read and drawn back so you can check it matches; if it does not, upload a clearer photo.
The reading can be wrong, especially with tall stacks, odd angles or glare, so always look at the drawn board first. A photo that cannot be read reliably is refused rather than guessed. The photo is not saved.
The best move and your chance to win
The dice are read from the photo (if they cannot be seen you pick them). The position is sent to GNU Backgammon, one of the strongest backgammon programs, and you get its best move and your chance to win after it, with gammons not counted. That lets you check a move from a real board and see why it is good.
What a pip count is
Each checker counts the number of its point, and a checker on the bar counts 25. The total is the number of pips a player has to play with the dice to bear everything off. The player with fewer pips leads the race.
An average roll is about 8 pips (doubles are played four times), so a difference of 8 pips is about one roll of lead. At the start of a game both players have 167 pips.
The 8-9-12 rule
In a pure race, when the checkers have passed each other, the lead as a percentage of the leader’s count tells you when to double. At 8% or more it is right to double, at 9% or more to redouble, and at 12% or more your opponent should pass. ZAR Lens shows this for the position it reads.
The rule is a guide, not a law: with heavy positions, or checkers on the bar or in your opponent’s home board, the right choice differs.