Increasing Velocity?

This problem's a bit more complex than my last entry. The code is supposed to let the user press one key and make the orange pixel run to either the left or the right depending on the key. However, if the user presses one of those two keys more than once, the pixel's speed in that direction increases to a point that it shouldn't. I really need help for this one. My code can be found here. PLZ HELP!
-LM
EDIT: It might be easier to just use:

pastebin get kVdJBS3c helios

The problem is here:

while true do
  os.startTimer(.5) --#new timer
  ev,a0,a1,a2=os.pullEvent()
  if ev=="key" then
    if a0==203 then
      hs=-1
    elseif a0==205 then
      hs=1
    elseif a0==15 then
      break
    end
  elseif ev=="timer" then
    if (x>1 and hs<0) or (x<w and hs>0) then
      xp=x
      x=x+hs
    end
    paintutils.drawPixel(xp,y,colors.black)
    paintutils.drawPixel(x,y,colors.orange)
  end
end

Your code starts a new timer each time any event occurs. I'd recommend starting a new timer only after the previous timer event was caught. It'd also be a good idea to check if the timer event is, in fact, the same timer you started. Otherwise, if the program was run in parallel with something else (probably by an OS), you might catch timer events from other programs.

THANK YOU! Now I can fix that issue! It didn't even occur to me that I should start the first timer BEFORE the loop. X'D