ContourPlot confusion

*To*: mathgroup at smc.vnet.net*Subject*: [mg116320] ContourPlot confusion*From*: kelly <kereidy at gmail.com>*Date*: Fri, 11 Feb 2011 04:13:23 -0500 (EST)

Hi! I'm plotting the following: ContourPlot[Expression[50, x, y] == 0), {x, -15, -17}, {y, -0.7, -0.5}] So some previously defined expression which is a function of 50, x, and y. I've set it to only show the "Expression = 0" contour, which it does. However, when I use "Get Coordinates" to get the coordinates of a point along this contour line & plug those coordinates back into the expression, it evaluates to around -33. Shouldn't it evaluate to 0 if the point lies along the 0 contour? Any help is appreciated! So confused!