The 20 board is the center board, with 19 boards on each side of it.  If there were an even number of boards then the head pin would be inbetween two boards.

The arrows line up with pin placement.  7 & 10 pins on the five board.  4 & 6 pins on the ten board.  2 & 3, and the 8 & 9 on the fifteen board.  1 & 5 on the twenty board.

Perfect angle for a strike is 6 to 7 degrees at the 17 board.

Here''s your link to everything you want to know about bowling: http://bowlingknowledge.info/index.php?option=com_content&task=view&id=181&Itemid=1

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Edited on 3/10/2010 5:44 AM

Actually, the arrows (aside from the 4th arrow) don''t quite line up with the pins.  The 4th arrow and the 1- and 5-pins sit centered on the 20 board.  

However, the 10-pin is positioned 2.75" from the right edge of the lane.  The lane has 39 boards and is 41.5" wide.  This puts the 10-pin on about the 3.1 board, the 6-pin on board 8.7, the 3- and 9-pins on board 14.4, the 2- and 8-pins on board 25.6, the 4-pin on board 31.3, and the 7-pin on board 36.9.

Edited on 3/10/2010 12:16 PM

Edited on 3/10/2010 12:17 PM

As for Targeting systems theres many. Heres the original info doesn't fully work with todays games. But is interest seeing how it developed.

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Rangefinder ® system by Brunswick

It was invented by Lowell Jackson back in the 1930's

 "Jackson's poor eyesight was responsible for his most lasting legacy.
Because he could not see the pins well, he would often put a pencil dot
on the approach to help line up. Eventually, a nitpicking official at a
tournament cited the ABC rulebook and made him erase his mark.

That got Jackson to thinking. Out on the lanes, bowlers had long used
darker boards to help them aim their deliveries. Why not have a series
of markers permanently inlaid on the approaches and lanes? Jackson took
his idea to his bosses at Brunswick. The result was the now familiar
rangefinder system, which the ABC approved in 1939, and which is still
in use today. "
Click
for more info on Jackson


The bowling lane and approach contain DOTS (dowels) and ARROWS which are
visual aids to proper alignment for strikes and spares. These aids are
positioned on numbered boards.

ON THE APPROACH
There are three sets of seven dots on the approach. The first set
located approximately 15 feet from the foul line the second set is 12
feet away and the third set is approximately 3 inches away. In some
centers, the outermost dots are missing at the 12- and 15-foot levels.
The center dot in each set is larger than the rest. You use the first
two sets to help you choose where to stand on the approach for strikes
and spares -- your SETUP LOCATION. The third set will help you or an
observer determine exactly where your ball touches down on the lane --
the TOUCHDOWN POINT.

. In order for all bowlers to communicate correctly, right-handed
bowlers need to count from right to left, while left-handed bowlers need
to count from left to right. For purposes of explaining strike targeting
below, we will limit the number of playable boards at 20. Therefore, the
sequence is 5, 10, 15, 20, 15, 10, and 5. We will change our
illustration when we talk about spare shooting.


How to use the RANGEFINDER ® targeting system
ON THE LANE
There is a set of SEVEN ARROWS located approximately 15 feet from the
foul line and a set of TEN DOTS located approximately six feet from the
foul line. These are parts of the RANGEFINDER ® targeting system
innovated by Brunswick during the second world war.  Note that the
approach dots and the lane arrows are in line with the pins, while the
lane dots are not.

Note-
The statement about the " arrows are in line with the pins" is incorrect.
As are a lot of the diagrams in the books of the lanes and pins.

While the 4th arrow lines up with the center of the headpin. As you move left or right from the center arrow, the arrows move off the pin centers and don't line directly up with them.

Here's a diagram showing how they really lineup.
Click here for Diagram
The black arrows are the lane arrows and the red arrows show where the dots lineup with the pins.

HOW TO TARGET FOR A STRIKE WHILE IN YOUR SETUP
You may use either the arrows or the dots as your VISUAL TARGET -- the
point where you fix your gaze. The following method uses BOTH -- the way
the Rangefinder ® system was originally intended to be used.

    1. First, choose your intended target line starting from the
approach dots at the foul line and ending with the arrows at 15 feet
your target line is approximately 15 feet long. Let's pick a 12-to-8
target line your ball touches down on board 12 and crosses board 8 at
the arrows. walk toward your target.

    2. Next, extend this path in your mind's eye all the way back to
your setup position on the approach. It crosses board 16 at the level of
your setup. walk toward your target.

    3. Position your bowling shoulder and your ball directly over this
extended target line. in this case, both would be over board 16, with
your forearm in line with your target. walk toward your target.

    4. Square your shoulders so that they are 90 degrees to your
forearm. walk toward your target.

    5. Square your feet perpendicular to your shoulders and parallel
with your target line to ensure that you will walk parallel with your
swing. walk toward your target.

    6. Since the lane dots at six feet are closer and easier to see,
drop your gaze back to these and use them as your visual target during
your delivery. Since these dots are closer to each other, you can more
effectively "fine tune" where you place your ball along your target
line. walk toward your target.

    7. When you start to move, make sure to push your ball toward your
target and walk toward your target.
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