Tangent additions using the “Inversion Operator”

 

0.25    +  0.25  =  +0.5     -2  (invert number and sign to get -2)

   +

   -2

   =

  -1.5     +0.666  (invert number and sign to get  +0.666)

 

Therefore:  0.25 + 0.25 = 0.666