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The lengths of the links comply with the conditions: E͞B=B͞F=a and E͞D=D͞F=b. Figure EBFD is a rhomboid linkage. Link 1 turns about fixed axis A and is connected by turning pairs B to links 2 and 3. Links 2 and 3 are connected by turning pairs F and E to sliders 4 and 6 which move along fixed guides p-p whose axis coincides with axis 0x. Links 5 and 7 are connected together by turning pair D and to sliders 4 and 6 by turning pairs F and E. When link 1 turns about axis A, point D describes a Cassinian oval with the equation (y²+x²)-2c²(y²-x²)=d⁴-c⁴ where d⁴=4(a²-b²)c²; a, b and c = constant dimensions of the mechanism. If d=c then point D describes a lemniscate of Bernoulli with the equation (y²+x²)-2c²(y²-x²)=0.