You found yourself with:
♠ A 8 4
♥ 5
♦ T 8 5 3
♣ K Q J 9 2
RHO opened 1♠ and you decided to overcall 2♣ because you are not vulnerable and want partner to lead it. LHO bid 2NT, showing an invitational raise or better with 3 or 4♠. Partner passed and RHO jumped to game. It is your lead.
The choice is obvious between the singleton or your own good-looking suit. A perfect problem to look at with the help of BC. You select the deal tab and enter the hand. Easy. Now the real difficulty starts. You must get the EW hands about right and also your partner's hand. He didn't bid 3♣. So, you have to exclude some hands. He doesn't have 4♣ with 6 or more points. Or 3♣ with 8HCP. Or 3♣ with 6 HCP and a singleton ♠. As you will notice when you use this tool these little subtilities make a difference. Therefore, it is always good to look at the hands of all players when you are testing the patterns. This is an iterative process.
You can inspect the hands with the preview button. But you could click on the Practice tab too and view the deals. Or you could use the Print/View option from the file menu. This offers you the best overview of all deals at once.
When you are satisfied you generate a lot of deals. Say 2000-5000 for a decent statistical result. The button 'Calculate DD' is now enabled. But before clicking it, make sure you fill the contract box right. In this case you set it to 4♠. East is declarer on a lead project as South is always the one who is on lead. You can set the vulnerability upfront, but you change it later. Clicking 'Calculate DD' will calculate the average number of DD tricks for each lead. The score is calculated afterwards.
The result screen looks like this:
There are three columns that give information about the lead. If you click on the headers of these columns it sorts by ascending or descending on that metric.
- Down. This column is sorted by the most likely lead to defeat the contract by default. This doesn't say it is the best lead.
- Tricks Declarer. Here you find the average number of tricks that the declarer makes on that lead. This can give you an indication about overtricks etc. Very expensive in a pair game but also in short team matches they add up.
- Imps vs. DD Lead. This column compares the lead for each deal against the best DD action on that deal. This way you can see what the long-term imp winner would be. But, life is short😉
As you can see there is no real winner. Sometimes you must cash or develop your club tricks before they disappear. Other times you are still safe to lead a club, switch to your singleton and reach partner with the ♣A. But if you remove the North patterns there will be a different outcome. It is always good to spend some time in defining what has not happened at the table. Things like they didn't overcall at the one level etc. It is very convenient to have some predefined pattern sets in your library. Then it is only a couple of clicks with a small modification now and then.