Mr Aiken also has some "housekeeping" matters to deal with.

One of these is in connection with the vital meeting of 14 June 2011 involving enterprise minister Arlene Foster, Dr Crawford and the department's energy boss Fiona Hepper, which resulted in the minister deciding to proceed with the RHI scheme.

Details of the meeting have proved very patchy, not least because minutes were not taken, and it's been central to much of the questioning of Dr Crawford and Mrs Foster over the past week.

Image source, RHI Inquiry

Mr Aiken is now able to produce Mrs Foster's electronic diary, which provides more detail of her appointments on the day in question.

This shows the meeting with Mrs Hepper was scheduled for 10:30 and the next appointment was set for 11:15, but Sir Patrick point outs that it's only a schedule and not a record of what actually happened.

Dr Crawford says he believes the meeting would've started at about 10:35 to 10:40 and would probably have run on to 11:30.

Image source, RHI Inquiry

Back for a fourth day before the inquiry, Dr Crawford is already in the witness chair and is taking questions from Mr Aiken.

Inquiry chair Sir Patrick Coghlin begins with another of his occasional comments on how the RHI Inquiry is viewed by the public outside the Senate chamber.

"If you think something sensational is being said, go to look at what the evidence is," he says.

"Don't prejudge what a witness is going to be asked about or is going to say until that witness has finished his or her tranche of evidence - that's the only fair way to do it."

Image source, RHI Inquiry

The inquiry's junior counsel Joseph Aiken says the "proper time to make judgements" is when "the inquiry provides its report, not on a daily basis arising out of particular testimony".

Today's witness Dr Andrew Crawford takes his chance to comment, saying that some of the media have been "selective in what they report".

But he's quickly shut down by the chair, who tells him: "Dr Crawford, I'm not inviting a comment from you."

BBC News Northern Ireland

Arlene Foster effectively wrote a "blank cheque" for the RHI scheme without knowing what the full cost would be, the inquiry heard.

Mrs Foster - the enterprise minister when the initiative began in 2012 - signed off a key document about the scheme in spite of it not containing a final bill for the project.

Image source, Pacemaker

Inquiry panellist Dr Keith MacLean said it was "inconceivable" he would have signed off on a project without assurances about the cost.

And he asked Mrs Foster former ministerial adviser Dr Andrew Crawford: "Why would you not, when you don't see that information, advise the minister not to sign a blank cheque?" he asked.

BBC News Northern Ireland

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a developing political crisis surrounding the scheme.

The RHI Inquiry began in November and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Pacemaker

It will look at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in 2015
• the scheme's closure

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the Democratic Unionist Party (DUP) leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, PA

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, more than a year on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.

The budget of the RHI scheme ran out of control because of critical flaws in the way it was set up.

Claimants could effectively earn more money the more fuel they burned because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

The most recent estimate for the overspend was set at £700m, if permanent cost controls aren't introduced.

The massive overspend bill will have to be picked up by the Northern Ireland taxpayer.

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's knowledge in late-2016... and the fallout from the scandal attached to it is still being felt in the region's politics today.

Image source, Getty Images

The scheme was set up by the Northern Ireland Executive in 2012, as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.

Welcome to Parliament Buildings at Stormont for Day 57 of the Renewable Heat Incentive (RHI) Inquiry.

If you were with us yesterday you'll know it was a fairly lively day at the office.

Image source, AFP

We'll be back in the old Senate chamber shortly as Arlene Foster's former ministerial adviser Dr Andrew Crawford slips into the witness chair for another all-day questioning.

Stick with us throughout the day for all of the action.