We refer to Joseph Chan's letter 'Octopus card users financially disadvantaged' (South China Morning Post, August 20). The $50 deposit required for an Octopus card is to guard against losses of the card which costs about $30, and also to allow a maximum negative value of $35 which enables passengers to complete the last journey even when the remaining value on the card is insufficient to cover the fare for that particular journey. MIRANDA LEUNG Creative Star Limited Hong Kong