Systems and methods for calibrating a bandwidth of a phase-locked loop are disclosed. An input screen for operating the touch panel is displayed on a display plane of the display portion, and an operating position of the touch panel recognizable on the display plane referring to the input screen. The reference image is written: IR1= withIR\u2062\u20621=\u2062with\u2062\u2062Rm=1N\u2062\u2211i,j\u2062I2\u2061-IN\u2061I1\u2061-IN\u2061,wherein IK represents the value of the pixel of the image IK detected by the pixel detector situated at the intersection of the row i and the column j of the detector pixel matrix, and N represents the total number of pixels in the matrix. The low-temperature circuit also includes a first heat exchanger for heating the second working fluid with heat from the first working fluid and a second heat exchanger for heating the second working fluid with heat from a second waste heat source. The positioning units position and restrict deformation of the frame when the frame is unfolded to be in use or is folded to be stored, to enhance the stability and user safety of the frame in use and render it convenient to store the frame.