O–C diagram of TU UMa. Black circles and blue stars display the maxima adopted from the GEOS database and new maxima determined in this work. The period decrease manifested by the parabolic trend (dot–dashed line) is obvious. Cyclic changes due to an orbital motion are also clearly visible. Our model of LiTE is represented by the solid red line. The top panel shows model 1 with all available data, while the plot in the bottom panel shows the situation with only photoelectric, CCD, and DSLR observations (model 2).