The player begins with a single unit-if that hand is won, 
the player has turned a one-unit profit, and the series 
ends.

If the player loses a hand, the wager remains the same 
until another hand is won, at which point it's increased 
by one unit. This continues until the player winds enough 
hands to recoup all previous losses, and come out one unit 
ahead, at which point the next hand is considered the 
beginning of a new series.

Here is an example of a series that persists for a dozen hands


# BET RESULT BALANCE 
1  1   LOSS   -1
2  1   LOSS   -2
3  1   LOSS   -3
4  1   WIN    -2
5  2   WIN     0
6  3   LOSS   -3
7  3   LOSS   -6
8  3   WIN    -3
9  4   LOSS   -4
10 4   LOSS   -8
11 4   WIN    -4
12 5   WIN    +1


In this sequence, the player wins 5 out of 12 hands - slightly 
less than the expected average - but concludes the sequence 
with a one-unit gain. The consistent-wager player would have 
emerged at a net loss of two units, and the Martingale player 
would have emerged with a net gain of five, but would have been 
required to bet as many as eight units on a single hand.