Sale
                
        
             
            Resonance Apparatus
            
                
                    $139.95
                
            
            $96.95
            
        
            I've been around awhile, and this is the only demo I've found (at a reasonable price) that shows differential thermal expansion of several materials. The zeroing mechanism is quick and simple, and the pointers are easy to see. Tip: Instead of using votive candles for heat, I mounted an aluminum heat shield under the rods, and use a heat gun to get them hot. They don't expand much, but it gets the point across nicely. Good job!