I have an old Avenir AC3 bike computer from 2000 for which I had to change the battery. Of course it forgot everything it knew, and needed reprogramming. And the manual was long gone. In searching the web I found nothing but misinformation, so just sat down and started fiddling with it. After 45 minutes of frustration, I finally put 2 and 2 together, so here it is. Hope this helps some one else.
My computer has 2 buttons. press the right one until you get to the screen that has the ODO reading. Then press and hold down the right button until it changes to a different screen, and the M/h (or KM/h) icon is flashing. You can then use the left button to choose which of these you want M/h is miles per hour, and KM/h is kilometers per hour. Press the right button, and the last digit of the 4 digit number below is now flashing. This 4 digit number is very important, and is how you set your computer to know what size tire you are using, and is THE CIRCUMFERENCE OF THE TIRE IN MILLIMETERS. You can find this in 2 different ways. You can measure the exact height of the tire fully inflated in MM, and multiply that by 3.1416 (pi), or you can do as I did, and put a metric tape measure on the ground, make a mark on the tire, then roll it 1 revolution next to the tape then see where it came to. My recumbent has a 20" front tire, and the measurement happened to come out to 1527mm. You can set this number one digit at a time on the ODO screen. Keep pressing the right button, and eventually you will get to the actual odometer reading. You don't have to change that if you want. The next press will bring you back to the normal screens. You can set the clock in a similar fashion. Get to the clock screen, then press and hold the right button until the time starts flashing, then set it with the left button. If you want to erase the trip information, and start a new trip log, get to the ATM screen (this is the time elapsed) then press and hold the right button, and press and hold the left button. The number will go to zero, and also DST (distance traveled) number on the next screen will go to zero as well as the AVS (average speed) number on the next screen. The odometer reading will remain unchanged.
Hope this helps somebody else. If you have one of these, don't throw it away just because you lost the manual. It is really a nice computer and very accurate once you get it properly set. If this has helped you, please write me, and let me know. Chris Foss firstname.lastname@example.org