Ive got this speed meter as well, but ive never seen a manual for it. P-O is the menu where you have to select the pulse width of the speed sensor i think? If you press the pulse button, you can cycle through the different pulse width settings. Im pretty sure the correct p value is 6? If it isnt, you will just get a speed reading which is out by some factor.
Then just press the speed button once to display your speed, or twice to display top speed i think.
To do a 0-400m run, you need to be stopped and press the 0-400m button twice. Then just drive and it will beep when 400m is up and show you the ET. press 0-400m button again to see your terminal speed.
Ive never pressed the trip button, may as well just use the odometer in the dash.
If you cant get any buttons to work, maybe take it apart and see if the wiring is still connected on the inside. Mine never used to show the third number in the speed (eg the 1 in 100) until i went in and played with the connections a bit.
Hope this helps,
Rhett