He found similar results for errors where the number of votes tallied is different from the number of voters registered as having voted in the official rolls; where the tallied total is different from the number of ballots in the box; and where the number of ballots in the box differs from the number of voters registered as having voted in the official votes. Taking into account the number of errors per polling place, again the results are very similar for all candidates. His conclusion is that there was no bias in the arithmetic errors (in other words, they were not present more often in the polling places won by one or the other candidate); he concludes that the errors were likely caused by the normal distribution of mathematical and organizational abilities of the randomly selected citizens in the polling place, and in the sometimes confusing design of the tally sheets and inadequate training of polling place workers. Counting votes in the official count In the official count López Obrador was ahead until late in the count. The official count does not use computers to count the votes. It tallies the totals from the actas as they are certified by the district boards. Every party has physical copies of every certified acta, and a representative in every district board. The votes were not counted randomly, but in order of the districts, with Mexico City, a López Obrador stronghold, coming first, and the pro-Calderón North coming last. See the PREP, Quick Count, and Official count sections of the article farther up. The IFE did not put up the official count results by precinct. The report of the Official Count online only gave the full running totals by candidate, obtained by adding results as they were reported at the district council level. The Official Count does not necessarily reopen the ballot packets and do a full vote-by-vote recount. It mostly only tabulates the numbers from the 130,000 sets of official paperwork (the "actas") for the hand counts previously done for all of the 130,000 precincts. Because the packets usually remain closed, some claim that much of the fraud and irregularities allegedly done at the precinct level would not be discovered by the official count. Although the representatives from any political parties in the district board may request that a packet be opened and recounted, this can only be done under specific sets