Deepening concentration moves on two axis - horizontal and vertical. Continuity, or staying over time, is the horizontal axis. Intimacy, or the movement toward dissolving the subject/object, is the vertical axis. Together concentration deepens.
The practice of samadhi requires commitment to wise effort towards concentration. it requires overcoming resistance to concentration, to be willing to feel intimacy with teh object. The fruit of commitment to concentration is one-pointed equanimity. Concentration can be considered om five different qualities from dedication to steadiness.