Is the '°' wrong in a degree centigrade mark? My PI helps to modify my thesis. He keeps changing the degree mark '°' to '0' as the superscript in a degree centigrade mark. He also changes every 'in the phase' to 'at the phase'.
As I searched, superscript 0 was used when initially creating the degree mark. But now ° is used in all the degree mark. 'Phase' means a period of time and in most paper and textbooks, people use 'in the phase'.
I'm confused about these changes. Is the '°' wrong, or 'in the phase' wrong? What do you use in the paper/thesis writing?

An example of using '°' and 'phase' in my thesis:
'The cells cultured at 30 °C for 3 days were in the stationary phase.' 'Stationary phase' is one of the cell-growth phases that range from several hours to several days.
Thanks to @Houska for your vision and practical suggestions &lt;3
Thanks to @AndreasRejbrand for correcting the degree sign to be 'U+00B0: DEGREE SIGN'. I have changed the sign in the title and body. In my PI's comments, he highlighted my degree sign (that I added through 'Symbols' in MS Word) and commented 'Should be a zero in superscript! Change all the rest.' So I believe he means using a zero.

PS. My PI is a Chinese who has been working in the UK for 20 years. His spoken English is fine, but sometimes he mixes up &quot;she&quot; and &quot;he&quot;, or forgets to add 's' in a verb with the third person.
For the International System of Units, the units of measurements are defined by the SI brochure. For the degree, unit of plane angle, and the degree Celsius, unit of Celsius temperature, the SI brochure at p. 133 and at p. 149 uses a circle and not a zero.
However, at table 8, the circle is rendered with an &quot;o&quot; (probably they didn't have the circle in that font). In any case, no zero.
You can refer your professor to that document. Further, if you're using LaTeX, you can use the siunitx package and write the angles with the command \ang and Celsius temperatures with the command \SI{23}{\celsius} (example with 23 °C). From the package documentation, you can see that also in this case the degree symbol is a circle.
If they still insist, let it go.