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Published8 min read
By Brian C., CPAP user since 2023Editorial standards

Why myAir Hours Don't Match Your SD Card

myAir and your SD card can show different hours for the same night. How ResMed counts a day, when myAir gets its data, and what to check.

ResMed's myAir app and a card reader like CPAP Clarity or OSCAR usually show the same hours for a night. ResMed counts a day from noon to noon, and CPAP Clarity and OSCAR follow it. When the hours differ, it is usually one of four things. You slept past noon, so part of that sleep counts on the next day. myAir got only part of the night, or none yet. A nap or a second session reached myAir later. Or you are comparing two different kinds of average.

How ResMed counts a day

ResMed's machines do not count from midnight. ResMed's support pages say your machine captures therapy data "from noon of one day to noon of the following day," because most people sleep through midnight and this keeps a night in one piece. The myAir report guide says the same thing in its own words. A sleep session starts at midday and finishes 24 hours later.

So everything from noon Monday to noon Tuesday is Monday's night. A session you start at 10 pm Monday and a nap at 9 am Tuesday both land on Monday.

The catch is noon itself. ResMed says that if you sleep through noon, your machine "will split the data across two days." ResMed notes this does not change your compliance figures, which are worked out across several days.

Say you work nights and sleep with the mask from 6 am to 2 pm. myAir shows six hours on one day and two on the next. That is not lost time; the last two hours are on the following day.

Card readers use the same day

The split can show on the card too. On an AirCurve 10 card we have read from someone who often slept past noon, the machine closed the session just before noon and started a new one at 12:00, so a card reader shows the same split myAir does.

CPAP Clarity places each session on a night by the noon line. A session that starts before noon belongs to the night before, and one that starts at noon or later belongs to that day. A night's hours are its sessions added together, so time the mask was off between two sessions is not counted.

OSCAR uses the same noon line for ResMed. On a profile with a ResMed machine it turns off its session-splitting options and tells you why with this message, "On ResMed devices, days will split at noon like in ResMed's commercial software." It also sets its day split to 12:00 and turns off "Combine Close Sessions" and "Ignore Short Sessions" when it first imports a ResMed card.

myAir gets its data separately from the card

This is the cause behind most mismatches. ResMed says myAir collects therapy data wirelessly, "independent from that stored on the SD card." The card and the app are two copies made in two ways, so one can have a night the other does not.

ResMed says the machine sends a night's data one hour after you stop therapy, as long as it is plugged in, out of airplane mode and has a mobile signal. It also says it can take several hours for the night to show on your myAir dashboard. If you switch the machine off at the wall right after you take the mask off, the night may arrive late.

Two more things affect what myAir shows.

  • A second session arrives later. ResMed says myAir shows the first sleep session of the day, and when another session is recorded for the same day it updates once that data arrives. If you check myAir in the morning before a nap or a later session has been sent, the hours may be lower than the card's.
  • Usage needs breathing. ResMed says usage hours require a breath to be detected. A machine running with nobody breathing on it adds no hours.

Averages are worked out differently

If you are comparing a 30-day figure rather than one night, check what each one averages over. The myAir report averages usage over the days you used the machine, not over every day in the period. CPAP Clarity's History counts short nights in its usage average and says how many it counted, while its AHI leaves them out. Neither is the Medicare check. Medicare's rule asks for 4 hours or more on at least 21 nights in any 30 days in a row in your first three months, so a skipped night counts against it in a way a days-used average does not show. Your equipment provider can tell you which figures they send.

How to find which one it is

Pick the night that disagrees and look at it on the card, then in myAir.

  1. Look at when the mask was on. On your night page in CPAP Clarity, the card called "Your night, hour by hour" shows the time the mask was on and any gaps between, when your card has the detailed data. If your sleep ran past noon, the hours after noon are on the next day, in myAir and in CPAP Clarity alike.
  2. Check whether myAir has caught up. If the card's night has more sessions than myAir shows, give myAir a few hours with the machine plugged in, then look again.
  3. Check for a missing night on one side. If a whole night is on the card and not in myAir, or the other way round, it is a sync gap or a card that was out of the machine, not a difference in counting.
  4. Compare like with like. For a monthly figure, make sure both are averaging over the same set of nights.

If the hours still disagree on a night that did not run past noon, and myAir has had a day to sync, it is worth asking your equipment provider to look at what the machine sent.

Common Questions

Why does myAir say I used my machine less than I did?

One common reason is that you slept past noon. ResMed's machines count a day from noon to noon, so the time after noon goes on the next day. myAir also shows only what the machine has sent so far, so a session after the last sync appears later.

Does CPAP Clarity use the same day as myAir?

For ResMed, yes. CPAP Clarity places each ResMed session on a night by the same noon line and adds a night's sessions together. On the AirCurve 10 card we checked, a sleep that ran past noon was already split into two sessions at noon, so it landed on two days in CPAP Clarity, the same split ResMed describes for myAir.

Why does OSCAR show different hours from myAir?

For a ResMed machine OSCAR splits days at noon, as its own preferences note says, and does not combine or drop sessions. When OSCAR and myAir disagree, the usual causes are the same as for any card reader, a night myAir has not received yet or a later session that arrived after you looked.

Can myAir have a night my SD card does not?

Yes. ResMed says myAir collects its data wirelessly, independently of the SD card, so a night can reach one and not the other, for example when the card was out of the machine.

How long does myAir take to show last night?

ResMed says the machine sends data one hour after you stop therapy if it stays plugged in with a signal, and that it can take several hours to appear on your dashboard.

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