2.1.668 Part 1 Section 18.4.11, sz (Font Size)
a. The standard restricts the definition of the sz element to Latin and East Asian text only.
Office does not restrict the applicability of the sz element to only Latin and East Asian text, that is, it applies to all text.
b. The standard states that sz is the point size to be used to display text.
Office converts the points provided to twips, and rounding may occur when writing sz@val back to SpreadsheetML files.
c. The standard does not specify restrictions on the val attribute.
Office requires the val attribute to be a double between 1 and 409.55 inclusive.