Which of the following statements is not correct?

The constant specific rotation in water which either $\alpha -D\mathit{-}$glucose or $\beta -D-$glucose attains is $+ 52.7°$. 

Glucose exists in two forms, i.e., α-D-glucose with a specific rotation of +1120 and β -D-glucose with a specific rotation of+190. However, when either of these two forms is dissolved in water and allowed to stand. it gets converted into the same equilibrium mixture of both the α- and β -forms with a small amount of open chain form. As a result of this equilibrium, the specific rotation of a freshly prepared solution of α-glucose decreases from +1120 to52.70 while that of β glucose increases from +190 to 52.70.