STACK is an online testing system that can automatically assess mathematical formulae. When working with STACK on a smartphone, inputting mathematical formulae is time-consuming; therefore, to solve this problem a mathematical formula input interface for smartphones has been developed based on the flick operation. However, since the time of development, an increasing number of smartphone types have been developed, making the verification of such interfaces important. We organised the problems of each device and verified the effectiveness of the flick operation for formula input compared with conventional text input. [For the full proceedings, see ED639391.]