     expr = expr.trim()
 
     # cell
-    if /^\w\d{1,2}$/.exec expr
+    if /^[A-Z]\d{1,2}$/.exec expr
       return getCalcResultAt expr
 
     # list of cells

      return [getArgValue cell for cell in cells]

    # matrix
    if /^\w\d{1,2}:\w\d{1,2}$/.exec expr
      refs = expr.split(':')
      colStart = refs[0][0].toUpperCase().charCodeAt(0) - 65 # A turns into 0
      colEnd   = refs[1][0].toUpperCase().charCodeAt(0) - 65


    # arithmetic (or number)
    try
      return eval expr.replace /([A-Z]\d{1,2})/g, (addr) ->
        getCalcResultAt(addr) or 0
    catch e
      return '#VALUE'
