Colfax Envelope Corp. (Colfax) (plaintiff) hired employees to operate its two printing presses. These employees were represented by Local No. 458-3M (the union) (defendant). Previously, the union would negotiate a collective bargaining agreement with the Chicago Lithographers Association (CLA) and send a summary of the terms to Colfax for approval. If Colfax did not agree with those terms, it had the right to negotiate separately. The collective bargaining agreement set the minimum manning requirements for each type of printing press. Colfax had two presses that were 78 inches wide and, under the existing collective bargaining agreement, had to be manned by four employees each. When a summary of the newest changes to the agreement was sent to Colfax, the summary listed one of the manning requirements as “4C 60 Press-3 Men,” which Colfax interpreted as requiring presses 60 inches or wider to be manned by 3 employees. Finding this advantageous, Colfax agreed to the changes in the summary. Upon receiving the final agreement, Colfax learned that “4C 60 Press-3 Men” meant 3 men were required for presses of 60 inches or less. Colfax sought a declaration stating that no collective bargaining agreement was created due to lack of agreement on an essential term. The union sought to compel arbitration because the agreement contained an arbitration clause. The trial court granted summary judgment finding that the summary unambiguously referred to 60-inch presses. Colfax appealed.