BMC Data Guide: E-20A and G3 A20

The BMC E-20A and the BMC G3 A20 write the same SD card format, so one guide covers both. CPAP Clarity reads that format in your browser: usage, AHI with the events behind it, pressure, leak, and the breathing measurements many machines in this price range do not record at all. Nothing is uploaded, and there is no account.

Two Machines, One Card Format

The E-20A is the auto-adjusting CPAP from BMC Medical, a Beijing device maker founded in 2001, common in the UK outside the NHS supply chain and often the machine people start therapy on while waiting for an NHS device.

The G3 A20 sits above it in the same product line and is the newer design.

Both write a proprietary binary set (a .USR file, an .idx index, an .evt event log and numbered waveform files) rather than anything you can open yourself, and the two are byte-compatible, which is why CPAP Clarity reads both through the same parser and why everything below applies equally to either. For a short summary of what you get, see CPAP Clarity for BMC.

The confusing part is the Luna G3. The G3 A20 and the React Health Luna G3 are the same physical hardware, sold under different names in different markets. They are not the same for data purposes, because the firmware differs and firmware decides the card layout. If your machine says Luna, read the Luna G3 data guide instead. If it says BMC, you are in the right place. For how these sit against other brands, see the machine comparison.

What Your Card Records

Every night the machine writes these to the card, and CPAP Clarity decodes all of them:

Therapy pressure, one reading per second across the night. The card also holds a separate exhale value, which CPAP Clarity decodes but does not chart today, so what you see is the inhale trace.

Mask leak, in liters per minute.

Breathing measurements. Respiratory rate, tidal volume (the air in each breath, in milliliters) and minute ventilation, all charted. This is the notable part: these are channels a lot of machines in this bracket never write at all. The card also carries your inhale-to-exhale ratio, which we decode and do not chart yet.

AHI with the events behind it. Obstructive apneas, central apneas and hypopneas, each counted and timestamped separately rather than pooled into one number.

Your settings. Mode, pressure range, Reslex level, ramp time and humidity, read straight off the card. Turning humidity up reduces dryness but can leave water in the hose, known as rainout.

The channels arrive as one value per second rather than a breath-by-breath trace, so you get a detailed night without a flow waveform.

What Is Not on the Card

Cheyne-Stokes respiration is genuinely absent: the format carries no marker for it, so there is nothing to decode. Flow limitation and a snore index are a weaker claim and worth stating precisely: CPAP Clarity does not show either, and we have not found either in the format, which is not the same as proving your machine never recorded them. There is also no breath-by-breath flow waveform to chart.

None of those are essential to reading your therapy. Usage, AHI, pressure and leak carry the weight, and this machine records all four plus the breathing measurements above.

Getting the Card Into CPAP Clarity

Power the machine off, then find the card. On the E-20A the slot is on the side opposite the humidifier, on the same panel as the air filter. On the G3 A20 it is on the humidifier side, so you slide off the water chamber to reach it. Power off first either way: the machine may still be writing the night you just finished.
Put the card in your computer or phone. Any SD reader works, and any name-brand card will do if you ever need to replace the one that shipped with the machine.
Open CPAP Clarity and drop the whole card in. Select the entire card rather than a folder inside it, so the parser can see all the files it needs together.
Read your data. It appears in a few seconds, in the page, on your own device.

There is no installation and no account, because the parsing happens in the browser. How to use CPAP Clarity has the walkthrough with screenshots.

Reading Your Numbers

Usage

Medicare's coverage rule defines adherence as at least 4 hours a night on 70 percent of nights across a consecutive 30-day period in the first three months. That is a coverage threshold rather than a clinical target. The Medicare rule covers how it is applied.

AHI and the split underneath it

An AHI under 5.0 is the range the AASM associates with well-controlled CPAP, a figure from its in-lab titration guideline rather than a home therapy target. Consistently above that, or a clear 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 what pressure is there to fix. Central events come from the drive to breathe and call for a different conversation. What is AHI? works through the categories.

Pressure and Reslex

Reslex is BMC's exhalation relief, the same idea as ResMed's EPR, with three levels. It drops the pressure as you breathe out so exhaling feels less like work. The card records inhale and exhale pressure separately, though only the inhale trace is charted today, so what CPAP Clarity gives you is the level you are set to rather than a picture of the relief itself. Understanding EPR explains what pressure relief does and does not change.

Leak

Some leak is intentional, since your mask vents on purpose. What matters is the unintentional kind from a seal that is not holding, because a bad enough leak stops the machine scoring events reliably. Try headgear tension and sleeping position before concluding you need a different mask. Fixing CPAP mask leaks goes through the usual causes.

The breathing measurements

Respiratory rate, tidal volume and minute ventilation are interesting to watch but are not numbers to self-diagnose from. They are most useful as a trend, and most useful of all in a conversation with your prescriber.

How These Numbers Were Checked

Event counts are cross-checked against OSCAR reading the same card, which is the bar every CPAP device on this site has to clear.

Session durations are the exception, and it is worth knowing why. For BMC cards, CPAP Clarity uses its own reading of the packet stream rather than OSCAR's, because OSCAR's BMC loader has a seek bug that undercounts duration. The packet timestamps are the machine's own record, so that is not a close call.

That one bug has knock-on effects, and glossing them would be the same overclaim in miniature. Because OSCAR seeks past frames, it also misses some events inside them, so our event counts can run slightly higher than OSCAR's on the same card, and our AHI slightly lower because it divides by a longer, more accurate night. Our regression gate allows for that rather than pretending the two agree exactly.

Only one E-20A card has been validated end to end so far. If you own one, importing yours genuinely helps.

One Known Dead End, Stated Plainly

Two E-20A sessions have hit an error where CPAP Clarity recognizes the card but cannot read its sessions. We have not been able to reproduce it, and without the card we cannot tell a gap in our parser from a damaged card. Both remain possible.

If that happens to you, you get an honest dead end rather than wrong numbers, which is the behavior we want when the alternative is guessing. It cannot be fixed without the card itself, so if yours does this, tell us. We use what you send only to build support for your device.

Do Not Change Your Own Settings

Seeing your pressure range and Reslex level explains a lot about your data. It is not an invitation to change them. Pressure is a prescription, and the useful move when the data raises a question is to bring the data to your prescriber.

Frequently Asked Questions

Can I read my BMC CPAP data for free?

Yes. CPAP Clarity reads the BMC E-20A and G3 A20 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.

Is the BMC G3 A20 the same as the Luna G3?

The same physical machine, sold under different names in different markets, but not the same for data. The firmware differs and firmware decides the card layout, so the Luna G3 writes a different format and has its own guide.

Does OSCAR read BMC machines?

Yes, and our event counts are cross-checked against it. We deliberately differ on one thing: session duration, where OSCAR's BMC loader has a seek bug that makes its figures coarse, so CPAP Clarity uses the machine's own packet timestamps.

Why is there no flow limitation or snore data?

There is no Cheyne-Stokes marker in this format at all, and no breath-by-breath flow waveform. Flow limitation and a snore index are a different case: we do not show either, and we have not found either in the format, which is not the same as saying your machine did not record them. The core metrics are all present.

Does the BMC record tidal volume?

Yes, along with respiratory rate and minute ventilation, and CPAP Clarity charts all three. These are channels many machines at this price never write. Your inhale-to-exhale ratio is on the card too, but it is decoded rather than charted today.

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-5.0 figure.
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 percent of nights adherence definition.