axis138Before calculating the heart axis, we must understand that each lead represents a different point of view of the same electrical stimulus.. To calculate the cardiac axis we will only use the limbs leads. Taking the exampleExca Zaxis 138 - Free download as Excel Spreadsheet (.xls .xlsx), PDF File (.pdf), Text File (.txt) or read on for free. The document lists parts for an Exca Zaxis 138 excavator including