Well, I did my occassional search for iPad or iPhone apps useful for math educators and this time I think I found a gem. Quick Graph was so good that within 5 minutes I paid the $1.99 to get access to implicit functions. I look forward to experimenting with it on an iPad later tonight.
Quick Graph creates beautiful graphs in 2D and 3D and renders the 3D graphs very quickly. It understands polar, spherical, and cylindrical coordinates. You do not have to change settings to use these. The calculator interprets r, theta and phi when you use them as references to the correct coordinate system. It comes with a library of equations to produce interesting graphs. You can save graphs you want to reuse to that library.
Ease of use is its biggest advantage over other graphers, however. The navigation is intuitive. On a graph the pinch zoom works as expected for iDevices. By default the zoom is proportional relative to all axes, but you can change that in the settings. I appreciate this because when using GraphCalc I frequently get uneven zoom that doesn’t help clarify. To add a function you press a + icon on the screen. To delete an equation you use the typical swipe and confirm.
You can export images. So far you can just export to your camera roll or to email. The email comes with the screen image and a list of equations used to generate the equation. The email is in html and in my mail client I had to view it in a browser before I could save the image to my desktop.
The only drawbacks I noticed in 30 minutes of experimentation is that either the calculator does not have calculate features like intersect and find maximum or these are very hard to find or use. Also, you cannot trace relations that are not functions, but this is not surprising if the trace is built on a drag along the x-axis.