Productivity equals success and any successful person will tell you that the key to productivity is taking measured steps. We should carefully monitor our activities according to the time and money we spend on them. After making our observations, their analysis will reveal which activities our resources are being concentrated on; having this information at hand can lead to better decision making and ultimately an improved lifestyle.
All of this simply cannot be done using a physical diary. A computer is the best way to go. More specifically, 1DayLater is what you should use.