m = peripheral.wrap("top")
m.clear()
m.setCursorPos(1,1)

local function centerText(text)
  x,y = m.getSize()
  x1,y1 = m.getCursorPos()
  m.setCursorPos((math.floor(x/2) - (math.floor(#text/2))), y1)
  m.write(text)
end

m.setTextColor(colors.red)
centerText("How to use Chest Shops!")
m.setCursorPos(1, 3)
m.setTextColor(colors.white)
centerText("Left Mouse Button = Sell")
m.setCursorPos(1, 4)
centerText("Right Mouse Button = Buy")
m.setCursorPos(1, 7)
m.setTextColor(colors.red)
centerText("What all the lines on sign means?")
m.setCursorPos(1, 9)
m.setTextColor(colors.white)
centerText("{Owner}")
m.setCursorPos(1, 10)
centerText("{Number of Items}")
m.setCursorPos(1, 11)
centerText("B x = Buy from {Owner} for x$; S x = Sell to {Owner} for x$")
m.setCursorPos(1, 12)
centerText("{Name of item (xID)}")
m.setCursorPos(1, 15)
m.setTextColor(colors.red)
centerText("To set your own Chest Shop:")
m.setCursorPos(1, 17)
m.setTextColor(colors.white)
centerText("Put a sign above wooden chest")
m.setCursorPos(1, 18)
centerText("Leave first line on the sign empty")
m.setCursorPos(1, 19)
centerText("And fill the 2nd,3rd and 4th line")
m.setCursorPos(1, 13)
m.setTextColor(colors.lime)
centerText("xID = ID of non-vanilla item")