# Non-equal spacing comparing between \left, \right and their \big equivalents [duplicate]

The following two examples differ only with that in the first \left and \right are used, and in the second they are replaced with equivalent \Biggl and \Biggr. But spacing differs slightly. Why?

$$\pi(n) = \sum_{m=2}^n \left \lfloor \biggl ( \sum_{k=1}^{m-1} \bigl \lfloor (m/k) \big/ \lceil m/k \rceil \bigr \rfloor \biggr )^{-1} \right \rfloor$$

$$\pi(n) = \sum_{m=2}^n \Biggl \lfloor \biggl ( \sum_{k=1}^{m-1} \bigl \lfloor (m/k) \big/ \lceil m/k \rceil \bigr \rfloor \biggr )^{-1} \Biggr \rfloor$$

• The example might be simpler: $1\bigl(\big|\bigr)1$ versus $1\left(\big|\right)1$ – egreg Sep 13 '15 at 14:44