Having dragged around the supermarket, one finally arrives at the line of checkouts and must now choose the correct (and most appropriate) line to join. There are many factors to take into account, each depending upon one's personal circumstances.

For example, if you are the whingy, whiney sort who believes that the grass is always greener on the other side and that the other line moves quicker, you would be best off joining the checkout at the end of the store. This is because if you only have a line on one side of you - 50% of the time your line will move fastest, whereas with a line either side of you, your line only moves fastest 33% of the time. A simple matter of probability over perception.

The added complication to this is that normally the Express Checkouts are at the end of the supermarket nearest the door and these often only allow for people with 10 items or less, people with cash, people with disabilities, people who've taken their elderly relative out for the day, in fact just about anything that doesn't include you. This therefore only leaves you the checkout at the furthest end of the store and therefore may mean a long walk back to the exit. Thus dashing your hopes of a quick exit.

A further complication to the Express Checkouts are that while they may intuitively appeal as being quicker due to the fewer items rule, they may well take a lot longer as they have more people using them. More people leads to more payments having to be made and this turns out to be the time consuming factor with people digging through wallets for their loyalty cards, money off vouchers, credit cards (if allowed) or just using it as an opportunity to get rid of all their loose change accumulated since last Christmas.

So having decided against the Express Checkout and given up hope of a quick exit, you might decide to enjoy the scenery around you. In this case try identifying the most attractive checkout member of staff, (obviously taking into account your sexual persuasion(s) as you will rarely find sheep employed at the supermarket except perhaps in rural areas where they just can't get the staff).

Alternatively if you're feeling a bit low and need a bit of competitive excitement, try finding a suitable candidate to play a game with. Some suggestions for games to play can be found here.

If the previous courses of action do not apply to you e.g. you're patient, happily married and non-competitive; then you may have to brush up on your maths to find which line will get you out of the store most efficiently. Some of the factors to remember:

• how many people are queueing in line already?

• how many goods do they have, requiring the beep-beep noise to be made by the assistant?

• how long will it take you to walk to the exit by comparison to any other checkout?

Having taken into account these (and any other factors you feel are relevant) you will by now have a rough estimate of how much of your valuable time each checkout will cost you.

Now is the time to apply the final multiplier by selecting the most appropriate description, from the following categories, for the person(s) in front. If you feel they could be from more than one category, err on the side of caution and take the higher multiplier. If you feel they do not apply to any of the categories then you can safely assume they are a normal person who is capable of using a checkout in a safe and efficient manner.

• student (x0.9) Their 26 cans of cheap baked beans can easily be processed through by the operator in 1/13 of the normal time.

• single male (x1.25) Will be inept when it comes to packing (placing all the soft items at the bottom of the bag and will insist on trying to chat up the underage checkout girl/boy.

• single female (x1.5) Emotional scarring from previous relationship and her self-perceived incompetence at the supermarket results in a lot of floundering.

• OAPs¹ (x1.75) Slowed by their unfamiliarity with post-decimalisation coinage, that they only have pennies to pay with, their insistence on telling the operator about how bread used to only cost tuppence a loaf, except when it was rationed during the war, and how we should never have entered the Common Market. Fortunately the OAP factor is usually only found on Thursdays (pension day).

• married woman (x2) A desire to prove her competence in a relationship by using all available money-off vouchers and therefore keeping the household budget low.

• mother with children (x3) Children will want to do the packing, mother will have to repack everything, and then get all the items reversed off the bill that the children put in the trolley without her seeing.

• family (x3.5) sames reasons as per "Mother with children" except that father will believe he knows best and therefore start packing, mother will demand repacking due to where the goods will need to be stored at home, children will need telling off for playing in the empty packing cases and eventually a family row will ensue.

• married male (x1,000) due to need to resuscitate checkout operator following the shock of witnessing this rarest of events.

Now reconsider whether you have already missed the opportunity of a perfectly good checkout, by being so indecisive and picky, that checkout 5 which was empty on your initial pass has now gained a full complement of customers. If you have made this mistake spend no more time quibbling and go immediately to the nearest checkout regardless of the number of customers, their items and anything else you have previously taken into consideration.