Font or typeface affects the readability of your thesis more than any other style element; and as with other elements of the thesis, the font must be consistent throughout.

Font style
If you prefer to use a serif font, you may choose either Times or Times New Roman. If you prefer a sans serif font, you may use either Arial or Helvetica. You must use the same font style throughout the thesis; including, e.g., lists, page numbers, headings and subheadings, chapter and appendix titles, and figure and table captions.
Font size
All running text must use a professional- looking type size; OGS requires using between 10- and 12-point type.
All symbols in the text, figures and tables must be typed or lettered, not handwritten.