unwanted changes formula to values

[hitch_hiker]

This occurs randomly but with enough regularity that I have apostrophe copies of equations in every spreadsheet I create. Simple book I'm working on at the moment has the following equation '= d3*b6/100 has worked for the last 4 months without a hitch, now the cell shows 3.68, I retype the equation it accepts the equation, I enter new data the cell changes to the right value, then reverts to value ( no evidence of the equation ). This sometimes happens on the first entry of data , but sometimes 2nd or 3rd or ???. I cannot give this to anyone to enter data, because they will not check if the value changes. This occurs on every spreadsheet I create, with or without macros. As I said if I create a formula , I always create a copy of the formula preceded with an apostrophe, and keep it usually on the same page but hidden or a "formula keeper"page. This time it has occurred on a non-essential book, This time it's the easy formula, but there is no rhyme or reason to which formula will lock out . any suggetsions?
I know I will be asked so the equations on the page are:

=VLOOKUP(B3,'master data'!A9:G354,4,FALSE)	=ROUND(D3*B6,4)
=D3*B6/100

 

[Alex Blakenburg]

I cannot give this to anyone to enter data, because they will not check if the value changes.

Have you actually tried to give this to someone else or tried a different computer to see if it is specfic to your computer ?
Do you have any Add-Ins running ? Can you try turning them all off ?

 

[hitch_hiker]

Thanks Alex,
it is not machine specific, it has been happening to me for at least 10 years, as I said every formula has a copy to make my life easier rather than recreating it. Recently started a new computer, no add ins, this particular instance there are no macros either within this book or within the "personal"( or whatever it is called ), previous machine only had Mr Excel xls to html add in, did not change the performance before or after adding it in. As I said it is random, however, the reason for my question, it is currently happening every 3 or 4 cases, the data entry is simple, use a drop down to select product , type in weight, output is custom EAN13 barcode made up as "prefix" "part no" "price(5 digits). checksum calculated essentially off-site, absolutely no connection to the spreadsheet. However, this is the example I am working with today, another time totally different book same random problem
.

 

[Alex Blakenburg]

What does this mean ?

checksum calculated essentially off-site, absolutely no connection to the spreadsheet.

 

[hitch_hiker]

the checksum for the EAN13 calculation is not done by this spreadsheet it is done by a different and not connected machine. It has no bearing on anything the program is doing.