public void setSign(String sign) {
				if (sign == null) signButtonGroup.clearSelection();
				else
				if(sign.equals(AData.PLUS)) signButtonGroup.setSelected(plusButton.getModel(), true);
				else
				if(sign.equals(AData.MINUS)) signButtonGroup.setSelected(minusButton.getModel(), true);
				
				if (signButtonGroup.getSelection()!=null) clearSignSelection.setEnabled(true);
				else clearSignSelection.setEnabled(false);
			}