Laerdal CPRmeter 2 Mode D'emploi page 17

Compression Feedback
On Soft Surface
If the CPRmeter 2 detects a compression that exceeds 60 mm (2.36"),
it will show the depth indicator below the target area. If a specific
CPR event requires CPR to be performed on a patient lying on a
mattress, slide a backboard under the patient and compensate for
the mattress softness by ensuring that for each chest compression
the area below the compression depth target lights up.
Warning
When performing CPR on a patient lying on a mattress, a backboard
must be used to limit the amount of compressed depth which is
absorbed by the mattress. Depending on characteristics of the mattress,
backboard and patient, the depth compensation does not guarantee
that the patient chest is compressed by 50 mm (2").
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