NEW YORK–Excitement swept the financial world Monday, when a blue line jumped more than 11 percent, passing four black horizontal lines as it rose from 367.22 to 408.85.

It was the biggest single-day gain for a blue line since 1994.

“Even if you extend the blue line’s big white box back many vertical lines, you won’t find a comparably large jump,” said Milton Vogel, a senior analyst with Merrill Lynch. “That line just kept going up, up, up.”

Despite such bullishness, some financial observers are urging caution.

“Given this line’s long history of jaggedness, we really should take a wait-and-see approach,” Fortune magazine associate editor Charles Reames said. “And even if this important line continues its upward pointiness, we must remember that there are other shapes, colors, numbers, and lines to consider when judging the health of the economy.”