It was not until 1529 that the two sides where brought together.. Philip of Hesse, a vigorous supporter of the reformation, brought both Luther and Zwingli to Marburg to try and sort out their division. Bucer attended the meeting and urged the two of them to settle their differences, suggesting that differences should be tolerated among evangelicals provided they agreed to recognize the Bible alone as the normative source of faith. Agreement was reached on everything… other than the Eucharist. The meeting failed. Bucer continued to walk the fine line between the two parties.
In 1530 the “four cities” confession was produced by the ‘Zwinglian’ cities of Strasbourg, Contance, Lindau and Memmingen. It affirmed that the “true body and true blood were truly eaten and drunk”, not mere bread and wine. Between March and May of 1536 Bucer and Luther, Melanchthon and Bugenhagen drew up the Wittenburg Accord. Regarding the Eucharist, the accord stated that body and blood were “truly and substantially present” and received during communion.
Now, this was clearly moving away from a Zwinglian position. Yet in Bucer’s explanation of the articles of the accord he defends his agreement with the statement that the body and blood are truly and substantially present. He affirms that “these things take place truly, essentially and effectually, not merely figuratively or in imagination.” However, he goes on to say that the actual bread in itself cannot be the Lord’s body (as Luther does). In other words Bucer believed that the truly and substantial presence of Christ could be a Spiritual presence. It was as valid as a bodily presence. Does this agree with Calvin’s position?
 Ibid pg367