This determines the size of the font used to print a label underneath the bars. Bars are automatically suppressed if text becomes too large, so it is advisable to use a small font size here.
Penna hwn faint y wynebfath a ddefnyddir i argraffu label o dan y bariau. Fe rwystrir bariau' n ymysgogol os ddaw testun yn rhy fawr, felly mae' n syniad da dewis maint wynebfath bach yma.