Resistance for the SPX is at the round-number 900 area, which is home to the heaviest out-of-the-money call open interest in the May series.

FORBES: Don't Sell This May

In fact, since the SPX burst above the round 1, 300 level on the first trading day of February, nearly 80% of the daily closes since that time have been between 1, 300 and 1, 333, and these remain support and resistance levels in the near term.

FORBES: May Options With Five-Week Expiration Cycle Could Create Headwinds

Whereas double lows or previous resistance areas made themselves known to the SPX, RUT and DJIA, it was an important round-number level on the MID that came into play last week, as the index made its first-ever run at 1, 000 on Friday.

FORBES: Bullish Case Looks Tight At Key Technical Juncture

Meanwhile, potential resistance levels would be the familiar round-number areas, such as 12, 000 on the Dow, 1, 300 on the SPX and 800 on the RUT.

FORBES: Days Of Technical Reckoning Ahead