I entered the following equation F=L/(4*pi*SQ(D)) It can solve for F ( L=3.828E26, D=1.5E11 ) with no problem. F=1,353.878 However, trying to solve for L ( F=1,353.878, D=1.5E11 ) results in DIVIDE BY 0. But after pressing C twice, the correct result is shown 3.828E26. If I retry solving for L again...