A forecasting model has produced the forecasts as follows: For the period of January, the demand is $120$ and the forecast is $110.$ For the period of February, the demand is $110$ and the forecast is $115.$ For the period of March, the demand is $115$ and the forecast is $120.$For the period of April, the demand is $125$ and the forecast is $115.$For the period of May, the demand is $130$ and the forecast is $125.$ What is the average error at the end of May?