restore previous versions
excel or all microsoft applications should store previous saved documents so you can recover an older version thats been saved previously, I had a scenario where I edited a spreadsheet, saved and closed, the following day I found I had made many errors and was unable to undo and did not have any old documents saved, there should be an option to select which saved file you desire with a time and date stamp
J. Holbrook commented
I second this, I thought it was a feature. I came here looking for how to get this feature.