code: def com_google_fonts_check_unitsperem_strict(ttFont):
    
    upm_height = ttFont["head"].unitsPerEm
    ACCEPTABLE = [16, 32, 64, 128, 256, 500,
                  512, 1000, 1024, 2000, 2048]
    if upm_height not in ACCEPTABLE:
      yield FAIL, (f"Font em size (unitsPerEm) is {upm_height}."
                    " If possible, please consider using 1000"
                    " or even 2000 (which is ideal for"
                    " Variable Fonts)."
                    " The acceptable values for unitsPerEm,"
                   f" though, are: {ACCEPTABLE}.")
    elif upm_height != 2000:
      yield WARN, (f"Even though unitsPerEm ({upm_height}) in"
                    " this font is reasonable. It is strongly"
                    " advised to consider changing it to 2000,"
                    " since it will likely improve the quality of"
                    " Variable Fonts by avoiding excessive"
                    " rounding of coordinates on interpolations.")
    else:
      yield PASS, "Font em size is good (unitsPerEm = 2000)."
docs: Stricter unitsPerEm criteria for Google Fonts.