What does front and back mean in CTL?

Best way to explain this is to take a tiny chart. See below a chart with only 6 candles.

 On the left side you see a tiny EU chart. Each candle or bar represent 1 hour of price movement. If you right click on the chart (or press CTRL-E) you can export the data behind this chart. On the right you see the exported data for this tiny chart.

The data in each column is a SERIE of data. For example we have a SERIE of opening prices.

1,40756    -   1,40832    - 1,40838 -     1,40748   -   1,40720  – 1,41014
position 1 – position 2 – position3 – position 4 - position 5 - position 6

The FRONT of a serie is the place of the first data in that serie.  In the above serie the FRONT is position 1 with holds the data 1,40756.

The BACK of a serie is the place of the last data in that serie. In the above serie the back is the last position, this is position 6 with holds the data 1,41014.

The first column in our tiny chart indicates when the candle was starting to take shape. The open price was fixed at 24.03.2011 @16h00. The value of the HIGH, LOW, CLOSE were only available when the next hour candle started.

A strategy runs from candle to candle. Take the following strategy.

strategy bar;
input lots = 1,maxloss=40,offset=0.0001;
begin
integer currentbar;
if back(close) <  front(close) then return;
currentbar := back(close);
if close[currentbar]>open[currentbar] then
begin
if short() then exitshort();
if not long() then buy(lots);
end;
if close[currentbar]<open[currentbar] then
begin
if long() then exitlong();
if not short() then sell(lots);
end;
end.

The strategy strategy runs at the end of each candle. In the following table you see the used values at each candle.  

currentbar	back(close)	front(close)	close[currentbar]	open[currentbar]
1	1	1	1,40831	1,40756
2	2	1	1,40838	1,40832
3	3	1	1,40749	1,40838
4	4	1	1,40720	1,40748
5	5	1	1,41013	1,40720
6	6	1	1,41242	1,41014

Take a piece of paper. Put it on the chart so you can only see the first candle. Take another piece of paper and cover the lines below so you can only see the first line.

1

1

1

1,40831

1,40756

Now move the paper so you can see 2 candles. On the above table cover all lines except the second one.
Now move the paper so you can see 3 candle. On the above table cover all lines except the third line.
..........

This is how the strategy runs from candle to candle.