[Image] **** 3. Selecting a command from the menu (bottom right of screen) - command word is inverted when pointed to. I am pointing at 'neutral,' a command to reset any control. **** define what you mean by a group of objects by specifying the action each member of the group can take and describing properties that distinguish each member of the group. Since there are many different instruments in an airplane, but they do nearly the same thing, l defined one class called instrument and created instances of that class for the different types of instruments. Each instrument is totally individual, but still retains the characteristics of the class. For example, each has its own location on the screen, a label for the instrument, and a value to display. Each instrument understands certain messages. Each does the same thing when it receives that particular message, but each instrument can be controlled individually. Each instance is different from another instance in the sense that each has different characteristics. However, each instance of the class called instrument has the same general form. A common example is the class of human beings. Every person is a human being, but each person may have different hair color, height, and weight. The airplane simulator uses the mouse, keyset, and the keyboard together to send messages to the airplane to control its instruments, The mouse controls the position of the stick for pitch and roll, and it is used to select items from a menu of commands. A menu is a list of commands that can be executed by pointing at the command word with the mouse and pushing a button (Picture number 3). The keyset controls the setting of the rudder pedals and throttle, and uses different combinations of the five keys to control other operations in the simulator. At this time, the user sets the controls and requests a display of the state of the airplane with these control settings. Later, I will have the airplane continually change state. Now that l have created the class airplane (the set of instruments and their display), I can create many instances, each running on a different computer. I hope to change the program so that other computers in the room can communicate with each other for a dogfight situation, complete with missiles and a working radar. The ultimate version of the simulator will have a more insteresting horizon that will change with the heading of the airplane (i.e., a total 360 degree panorama can be seen, including mountains and rivers) complete with perspective so that the actual position of the airplane relative to objects is more apparent. **** 4. The whole screen is inverted - black changes to white and vice versa, **** Smalltalk is a very easy language to work with, with no limits to the complexity of programs. The concept of classes and instances is a very powerful idea and can be used very easily to simplify very complex problems. This is just not possible in Basic, no matter how advanced the version is. Therefore, a normal Basic program will probably look more complex than the same program written in Smalltalk, and, therefore, most likely harder to understand. The line-by-line execution of Basic is harder to understand, with the problem of if. . .thens and gotos interrupting the flow of the program. If this simulation was written in Basic, just for the instruments there would have to be vectors storing the values of the instruments and their labels, since all variables are local in Basic, and any part of the program that would access the instrument's data would have to know which vector and what element of the vector. ln Smalltalk, only the class would have to know the explicit details of where all the data was. By using nesting and different levels in the program, Smalltalk eliminates the problem of having to jump around in the program because of a conditional statement or goto. Overall, I think that Smalltalk is easier, more efficient, and more interesting to use than Basic. **** [Image] 5. Just before a crash, You can't see the horizon because the airplane is facing the ground.