Changed font doesn't display correctly in existing workbook

I have a workbook that was created using the Calibri font, a sans serif font. The text fields have mixed case and you can't tell the upper case "I" from the lower case "l" etc. The solution would be to use a serif font like Times New Roman, or a Courier. However, on this sheet when I select text, or the whole sheet for that matter, the font choice box shows the choice I have made, but the text in the spreadsheet does not change.

I can make the change in other worksheets, just this one specific file doesn't work.

I have looked through the options but I must be missing something.

Problem solved.

It has to do with screen resolution. The problem sheet was opening up with a screen magnification of 60% while the others were opening up at 70% or larger. I noticed that the formula window was showing the correct font but it was not correct in the cell. Changing font size and/or screen magnification caused the problem to appear or not.

Thanks for reading.