Entering a spread like APM7-2EPM7 into a DOMTrader window will show prices in increments of whole numbers (1100, 1101, 1102, 1103, etc). To change this to increments of 0.5 or other value you can do the following:
1) In the DOMTrader window right-click on the tab at the top where you see APM7-2EPM7 and select "Create QFormula".
2) Right click on that tab again and select “Edit QFormula”. This will open the Formula window.
3) In the formula window, highlight the formula (which should show as SPREAD(APM7-2*EPM7).
4) Click on "Setup" at the bottom of the window and change the Tick Size from Auto to 0.5
5) Click OK