S1 is louder at the apex. When an S wave is present in all of the limb leads the frontal plane axis is indeterminate. UNI EN ISO 20345 = Personal Protective Equipment â Specifications for safety footwear for general use. As per BTI: (XX) available in three versions: S1 for 42.7mm, S2 for 22.7mm, or S3 for 22.1mm mounts Then each mount version has 2 versions for different chain ring sizes, plus there are dedicated top pull and bottom pull versions of ⦠Given strings s1, s2, and s3, find whether s3 is formed by an interleaving of s1 and s2. Start studying Heart Sounds S1, S2, S3, S4. Keep in mind all of the S-types require Greens to fix (not had s1 or s2 planes but is the case for s3). EKG monitor: if the patient is on a bedside monitor the r-wave of the QRS complex will correlate with the sound of S1. Quote from DANIEL-CRO: S1