when converting ACT to SAT should i compare percentiles to get a score?

Test Preparation ACT Preparation
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<p>31 english is ~680, 28 in math is ~670 and a 31 in writing is 690 according to this table which gaTech uses: [url=&lt;a href=“http://www.act.org/aap/concordance/]ACT-SAT”&gt;The ACT Test for Students | ACT]ACT-SAT</a> Concordance<a href=“writing%20table”>/url</a></p>