If the cell is blank don't give any feedback.
If the cell has the right answer say it is Correct.
Otherwise say it is Incorrect.
There is conditional formatting as well. The Correct response is in green and bold. The Incorrect response is in red and Italic.
Then I use IF in plotting my graphs. This allows a graph to be built up from scratch as students answer questions that pertain to the information in the graph.
These two features in conjunction, plus that Excel can be used to display text in a readable way, particularly if you fill the cells with a white background, allows the homework to be a mixture of presentation of ideas and assessment of understanding those ideas, in one coherent whole. All of this makes sense to me and I've viewed this as far superior to what can be done with an LMS quiz tool.
Further my approach is for them to do it till they get all the questions right - no partial credit. At the end of the last worksheet a code is generated if all questions are done correctly. They are to copy the code and paste into a linked Google form. In the Google form they also enter their assigned course alias as a second check, so I can identify who they are and give them credit for completing the assignment. There is also a paragraph box so they can enter comments on the homework. I find that particularly useful, as I can react to the comments when we go over the homework in class.
The workbook asks them to choose their alias and enter their NetId up front. Part of this is to give individualized values to the parameters in the homework. The other part is to use in generating the code. Here is an example of what that looks like. I entered netid into the cell that asks for that information. This is for a homework on bargaining. neti is the first four letter of the NetID. 5 is a number that indexes the alias chosen.
Now for the issues. Here are a couple of comments from the homework due last night.
I posted it twice, because it always says to copy and paste. However, the excel file never allows me to copy the key so I just type it in instead. The double entry just provides a peace of mind that I put it in right.
I had problems with one of the entries. It kept converting my answers to dates for some reason.
I don't know how to troubleshoot these, as I can't replicate the problems on my machine at home. Then, yesterday, I had an eager beaver student who was already working on the homework due next week. He was having some trouble with it in that the feedback didn't seem to be working properly for him. After some back and forth in email I asked him to send me a copy of the file he had completed.
I don't know how this happened, but the file had lost its xlsx extension. Some of the feedback IF commands had lost the cell references to be used and likewise the graphs were screwed up too.
I didn't say this above but my worksheets are password protected and the cells with the feedback are locked, so students shouldn't be able to get into them or see the formulas. They should only see the output from those formulas. This instability manifested in spite of the precautions I had taken.
I don't know what I will do if problems of this sort persist. I feel quite out on a limb, as there is no community of like-minded instructors doing similar things with Excel. Microsoft has a page aimed at troubleshooting formulas in Excel. It is insufficient to address my issues. I know how to troubleshoot my own formulas as I create them. The Microsoft page is really about that. What I can't figure out is what happens on the student's computer to break a formula that works on mine.
If this were all Mac versus PC issues, at least I'd have an explanation. I think some of these problems are happening when the student uses a PC as I was helping one student outside of class and she had some of this instability on her laptop. (I create these at home on my Sony Vaio in Windows 7, Excel 2010.) Possibly the version of Excel matters here. Some students may be using Excel 2013. I have that on my new Vaio ultrabook. Maybe I should try to complete my homework on it, to see if there are difficulties. But doing that sort of thing is a stab in the dark.
I will say my prayers and bow to the computer gods. I'm not sure what else to do.