Luna G3 Data Guide: Read Your SD Card

Your Luna G3 writes every night of therapy to the SD card in the back of the machine, and you can read that card for free in a web browser. CPAP Clarity decodes the Luna G3 format directly on your own computer or phone: usage hours, AHI with the event breakdown behind it, the pressure the AutoCPAP algorithm chose, and mask leak. Nothing is uploaded to a server.

This guide covers where the card sits, what the machine writes to it, how to import it, and how to read the four numbers most owners care about. If you are still deciding whether the machine is right for you, the Luna G3 review covers the buying side. For a short summary of what CPAP Clarity shows for this machine, see CPAP Clarity for the Luna G3.

Where the SD Card Is on a Luna G3

The card slot is on the back of the machine at the humidifier end, immediately next to the transfer box that connects the water chamber. It takes a standard full-size SD card rather than a micro SD.

Power the machine off first, then push the card in to release it. Avoid pulling a card out of a running machine: it may still be writing the current session, and an interrupted write can cost you that night.

What the Luna G3 Records

The Luna G3 is an auto-titrating CPAP. It raises and lowers pressure through the night inside the range your prescription allows, and it logs what it did. CPAP Clarity decodes the following from the card:

Usage hours. How long the machine actually delivered therapy each night. This is the number insurers look at, and the one Medicare's coverage rule is built on.

AHI, and the events underneath it. Obstructive apneas, central apneas, hypopneas, and unclassified apneas, each with timestamps. Respiratory-effort-related arousals (RERAs) are decoded too and shown in your event breakdown, but they are excluded from the AHI figure, which matches how the machine itself reports.

Therapy pressure. One pressure value per second across the night, so you can watch how the algorithm responded rather than reading a single summary number.

Mask leak. One value per second, in liters per minute. CPAP Clarity flags nights where leak ran high and charts the trend across nights.

Your machine settings. Therapy mode, pressure range, mask type, tube type, and ramp time when it is not set to auto, read off the card rather than retyped by you. Reslex level and humidity are NOT shown, and the reason is worth knowing: the only place we could read them turned out to be the device's factory defaults rather than your actual configuration, so two contributors' cards both reported settings neither of them was using. CPAP Clarity now leaves those rows out instead of showing you a number that is quietly wrong.

Session timing. Start, end, and duration for each night.

The event mapping was checked against OSCAR 2.0's own reading of four contributor cards, matching exactly on 188 of 196 nights across all five event types. CPAP Clarity has been checked against three Luna G3 firmware families: G3-2.SC.73.04, G3-2.00.77, and G3-2.11.02.33.

What It Does Not Record

Coming from a ResMed machine, these are the channels you will notice missing. Some are genuinely absent from the format and some are things we have not been able to verify well enough to show; the difference is called out in each case.

Tidal volume and minute ventilation. On the newer firmware the breath-by-breath flow signal is on the card, but turning flow into a calibrated volume in milliliters needs manufacturer-app figures to check it against, and no contributor has been able to supply those. On the older firmware the positions the format reserves hold zero or non-physiological values. Either way we show nothing rather than a volume we cannot check.
Respiratory rate. Absent on the legacy G3-2.SC.73 firmware. The newer G3-2.11.x family does not store a rate either, but it does write a per-breath log, so CPAP Clarity works the rate out from that.
Flow limitation index. The event log carries a couple of codes that may be flow-limitation flags, but nothing has confirmed what they are, so we do not chart them.
Snore index and Cheyne-Stokes respiration. Not shown. We have not found a channel in this card's event log that we can stand behind for either one.

None of those missing channels changes how you read the four that are here. Usage, AHI, pressure, and leak are what the therapy is judged on.

How Many Nights the Card Holds

Two different windows sit on the card, and mixing them up is the usual source of confusion.

The detailed waveform buffer is short. It rolls over, keeping roughly the last 10 nights on the current G3-2.11.x firmware. The older G3-2.SC.73 generation writes 35 waveform files, about a month's worth, though files and nights are not the same thing: the one legacy card we have seen covered eight weeks in those 35 files. Once a night rolls out of that buffer, the breath-level detail behind it is gone for good.

The nightly summary history is much longer. One contributor's card carried 241 nights of dates, usage and event counts going back eight months. Those nights still import, with their real numbers, just without the waveform.

So a first import usually recovers far more history than people expect. If you want to keep the detail as well, import every week or two rather than monthly, because everything you import is stored in your own browser and survives the card overwriting itself.

One thing worth knowing before you go looking for a bug: a field can legitimately come up empty. Leak is read differently on each firmware generation, and where we have not validated a reading for your particular firmware, CPAP Clarity leaves it blank rather than showing a number it cannot vouch for.

Importing the Card

Power the machine off and remove the card as described above.
Put the card in your computer or phone. A built-in slot works. If you do not have one, an SD reader costs a few dollars, and on a phone you want a reader that matches your charging port.
Open CPAP Clarity and drop the whole card in. Select the entire SD card, not a folder inside it and not individual files. The format is detected automatically from the files present.
Read your data. Everything appears in a few seconds, in the browser, on your device.

There is no account, no installation, and no upload step, because the parsing happens in the page itself. If you want the walkthrough with screenshots, see how to use CPAP Clarity.

Reading Your Numbers

Usage hours

Medicare's coverage rule defines adherence as at least 4 hours a night on 70% of nights across a consecutive 30-day period, within the first three months of therapy. That is a coverage threshold rather than a clinical target, and plenty of people benefit from more. Our compliance guide covers how the rule is actually applied.

AHI and the split underneath it

AHI counts breathing disruptions per hour of use. An AHI under 5.0 is the range the AASM associates with well-controlled CPAP, a figure that comes from its in-lab titration guideline rather than from a home therapy target. Consistently above 5.0, or a sudden change from your own normal, is worth raising with the clinician who manages your therapy.

The split matters more than the total. Obstructive events mean the airway is collapsing, which is the thing pressure is there to fix. Central events come from the drive to breathe rather than the airway, and they call for a different conversation. CPAP Clarity shows both separately. What is AHI? goes through the categories properly.

This machine's event map has been rebuilt twice off contributor cards, so if your breakdown looks very different from what a sleep study or another tool showed you, please tell us.

Pressure and Reslex

Watching the pressure trace tells you how hard the machine worked. A night that sits low and flat with a good AHI means the algorithm found a comfortable working range. A night pinned near your upper limit with events still coming through means it ran out of room, which is a useful thing to bring to an appointment.

Reslex is BMC's exhalation relief, the equivalent of ResMed's EPR, with three levels set on the machine. You will not see your level in CPAP Clarity, for the reason given above, so if it matters to a conversation with your provider, read it off the machine's own menu. Understanding EPR explains what pressure relief does and does not change.

Leak

Some leak is intentional: your mask vents CO2 on purpose. What you are watching for is the unintentional kind from a seal that is not holding, because a mask leaking badly enough can stop the machine scoring events reliably.

If leak is persistently high, try headgear tension and sleeping position before deciding you need a different mask. Fixing CPAP mask leaks works through the usual causes in order.

Do Not Change Your Own Settings

CPAP Clarity shows your pressure range, mask type and ramp because seeing them explains a lot about your data. It is not an invitation to change them. Pressure settings are a prescription, and the right response to data you do not like is to bring it to your prescriber, which is far easier when you can show them a month of it.

Frequently Asked Questions

Where is the SD card slot on the Luna G3?

On the back of the machine at the humidifier end, next to the transfer box that connects the water chamber. It takes a full-size SD card. Push the card in to release it, with the machine powered off.

Can I read my Luna G3 data for free?

Yes. CPAP Clarity reads the Luna G3 card in your browser at no cost, with no account and no subscription. The card is decoded on your own device and your therapy data is never uploaded.

Does OSCAR read the Luna G3?

Only the newer OSCAR. Stock OSCAR 1.7.2 and earlier cannot open this family at all; OSCAR 2.0, released in June 2026, added a loader for it. Our event counts are checked against that 2.0 loader night by night across all five event types, so the two agree, but if you tried an older OSCAR and it refused your card, that is the reason.

How many nights does the Luna G3 card hold?

Two answers, because there are two windows. Detailed waveform is a short rolling buffer, roughly 10 nights on the current firmware, and 35 files (about a month) on the older generation. Nightly summaries go back much further; one contributor's card held 241 nights. Import every week or two to keep the detail, since anything you import stays in your own browser.

Why does my Luna G3 show no tidal volume or flow limitation?

Because neither has been verified to the point where we would put a number on screen. For tidal volume the flow signal is on the newer cards, but converting it to millilitres needs manufacturer figures to check against that nobody has been able to supply. For flow limitation the candidate markers have never been confirmed. In both cases we show nothing rather than a figure we cannot stand behind.

Does this guide cover the BMC G3 A20 as well?

Not quite, even though it is the same hardware. The G3 A20 runs a different firmware generation that writes a card in BMC's own format, and CPAP Clarity reads it through the BMC parser rather than the Luna one. Both machines import fine; the card layout is what differs. If yours says BMC G3 A20, read the BMC data guide instead.

Primary Sources

Kushida CA, Chediak A, Berry RB, et al. Clinical Guidelines for the Manual Titration of Positive Airway Pressure in Patients with Obstructive Sleep Apnea. J Clin Sleep Med. 2008;4(2):157-171. PubMed 18468315 (opens in new tab). The AASM guideline behind the under-5 figure cited above.
CMS Local Coverage Determination L33718, Positive Airway Pressure (PAP) Devices for the Treatment of Obstructive Sleep Apnea (opens in new tab). Source for the 4 hours a night on 70% of nights adherence definition.