Sunday, four in the afternoon, the picanha is gone and only the sausage is left. Someone complains about the boss, the other complains about the salary, and out comes the line: “we should open something together”. Everyone laughs. Monday morning, a message arrives with a listing for a shop space to rent. Three months later, the two of them are at the notary's office with a partnership agreement in hand.

Sometimes it is the childhood friend. Sometimes it is the brother-in-law, which turns Christmas into a risky event. Sometimes it is the colleague you always agreed with about everything, back when the decisions belonged to the boss. In every case, the partnership starts on top of another relationship, and that other relationship has almost never been tested by money, deadlines and losses.

Anyone who has ever had a business partner knows what happens in the first bad month. The qualities that made the friend great company at the barbecue — the improvising, the generosity, the optimism — turn, on the spreadsheet, into the partner who promises what he cannot deliver.

This is the ground that comparing two charts describes. The post about astrology at work deals with boss and employee, a relationship with hierarchy. Here the two stand on the same step, and neither can fire the other. The technique is the same one used for couples, synastry, with different questions.

I will start with the limit, because here it protects both sides, and also the people who will work with you.

No chart reading replaces a contract, a lawyer, an accountant and a financial analysis. The partners' agreement — who leaves, who buys whose share, what happens if one falls ill or wants out — is written with a professional, and it is written before it is needed. The chart does not know whether the shop gets foot traffic, whether the margin works, or whether the supplier pays on time.

The chart also does not decide who you sign with. It describes how two people tend to function together, and the decision to enter a partnership is still made with numbers, with conversation and with each person's actual track record. Choosing or rejecting a partner by birth date trades due diligence for superstition.

And you do not get a partner's chart done without him knowing. The reading needs the date, time and city of birth for both of you, and the time is a request made openly. By far the best use is with both of you reading it together before signing, as part of the conversation about how you will run the company.

One wants a neighbourhood bakery, with a queue at the door and his name on the awning. The other, without saying so, is already picturing the third branch and the sale to a bigger group in five years. Both said “let's open a bakery”, and both meant it.

In looking at two partners, this is the first question: are the two of you building the same thing? It is read by comparing each person's Sun with the other's Sun, Midheaven and house 10, with Jupiter and Saturn coming in to show the pace of growth each one can tolerate. The Midheaven is the point of public ambition, of the name each one wants to have in the world.

When one person's Sun falls in the other's house 10, that partner tends to become the face of the business, and the other feels either represented or erased, depending on the rest of the chart. When the two Midheavens point to very different places, the partnership works well at the start and begins to creak on the day it must choose between growing and staying the size it is.

None of these combinations rules out a partnership. They say which conversation needs to happen at the start, over coffee, before it happens in year three, with a lawyer.

Half past eleven at night, a message arrives: “I was thinking, I reckon we should change suppliers”. One of them has already replied with three suggestions. The other will only answer tomorrow, after reading it, doing the maths and sleeping on it. To the first, the second's delay looks like indifference. To the second, the first's rush looks like recklessness.

Mercury describes how each one thinks, negotiates and decides. In the comparison, one person's Mercury is placed next to the other's Mercury, Sun, Moon and Saturn, and the house 3 received comes in too. That is where it shows whether your meetings produce decisions or produce exhaustion.

One person's Mercury touching the other's Saturn, for instance, tends to describe the partner who always feels he has to justify every idea, and the other who feels he is the only one thinking about the risks. Both are right about what they feel. The fix is usually simple, once agreed: what kind of decision each one makes alone, which one needs a meeting, and which one waits for the next day.

This is also where you can see who negotiates better with suppliers and clients, which is already halfway to the next section.

Every partnership has a task nobody wants to do. The invoice, chasing the client who is late paying, the stock spreadsheet, the hard conversation with an employee. In the first months, whoever does it is whoever gets bothered first. By the second year, that person is exhausted and resentful, and the other does not understand why.

The division of roles is read in house 6, and in each chart's Saturn and Mars in relation to the other. Mars shows who takes the initiative, who opens the shop at six, and who chases the client. Saturn shows who holds the process, the deadline and the rule together. House 6 shows the routine each one can handle without dying of boredom.

The material of each chart comes in too: the element and modality that are in excess and in short supply in each one. In a partnership this has a very concrete translation. The element missing in both is the work neither of you will want to do. Two partners with no earth in the chart can have a brilliant idea and not a single invoice issued; two partners with no air can have a flawless product and no client knowing it exists.

Knowing this early opens two honest paths: split it on purpose, or hire someone to do it. Both beat leaving the task to fall on whoever gets bothered first.

End of the first year, some money is left over. One wants to reinvest it all and buy the second machine. The other has back rent to pay and wants to raise his drawings. Both are right, and this is how most partner fights begin.

The 2nd house describes each person's relationship with their own money: security, spending, what they value. House 8 describes the money that belongs to both, the shared risk, the debt, someone else's capital. Venus, Jupiter and Pluto come in to show each one's appetite for risk and how much each one trusts the other when the money is shared.

When one person's planets fall in the other's house 8, the subject of money between the two of you tends to carry weight, for better and for worse: it can be the trust of handing over the bank password, and it can be the feeling that the other decides alone about what belongs to both. The post about astrology and money explains the individual relationship with cash; here what matters is where two of those relationships meet in the same till.

None of this says whether the business will turn a profit. It says how the two of you will feel, and what you will each want to do, when it does and when it does not.

A good partnership in a good month is easy. The test comes in the month revenue drops by half, the big client cancels, and someone has to decide whether to lay off, cut costs, or put in more money. It is the month the barbecue friendship finds out what it is made of.

In the reading, the challenges are read in the contacts between Saturn, Mars and Pluto across the two charts, and in tense aspects generally. Mars square Mars tends to describe two partners who both want to be in charge at the same time. One person's Pluto over the other's Sun tends to describe an intense partnership, where one tends to concentrate control and the other, sooner or later, feels swallowed up. One person's Saturn over the other's Sun describes the partner who applies the brakes and the partner who feels held back.

None of these contacts is a sentence. Plenty of long partnerships have all three. What the reading offers is the name of the conflict before it arrives, and that changes the conversation: you can agree, calmly, on who has the final say in each area, and put it in the partnership agreement.

What I do in a consultation is name the tension honestly and show how it becomes a tool. A partner who applies the brakes, when that is his role and it has been agreed, is the reason the company still exists in year five.

The partnership does not erase the relationship that came before it. The childhood friend is still the childhood friend in the budget meeting, and the brother-in-law is still sitting at the Sunday lunch table, now with the spreadsheet on his mind.

This cuts both ways. The trust that already exists saves months of suspicion, which is why so many good partnerships start between friends. But closeness also lets things slide that a stranger-partner would never tolerate: the delay, the drawing taken without notice, the decision made alone. With a friend, the reckoning comes later, and it comes bigger.

What helps is keeping the roles separate, on purpose. Set a fixed day to talk about the company and keep the barbecue free of business. Have the division of roles written down, so nobody has to chase the friend, only the role. And accept that, if the partnership ends, the friendship has a better chance of surviving if the ending is written down too.

Reading both charts helps you see where the two relationships blend together. A strong Moon contact between the two, for instance, describes real affection, and also the difficulty of saying "no" to someone you love, which costs dearly in a company.

The word we use for company holds a scene quite close to the barbecue. Company comes from the late Latin companio, formed from with and panis: a companion was, literally, the one you shared bread with. Before it was a contract, partnership was a table.

It is worth doing an exercise with this image before signing anything. Sit down together, without rushing, and each of you writes the answer to five questions on your own: what I want this company to be in five years; how much I can afford to lose; which task I refuse to do under any circumstances; how I decide when I am in doubt; and what I do if I want to leave.

Then swap the pages. The answers that match are the foundation of the partnership. The ones that do not match are exactly what the chart helps you understand, and what the lawyer needs to put in the contract. It is the best time to find this out: with the bread still on the table.

And the questions that come up most on this subject, with the short answer: