Extract by mask changes the values

Discussion created by deanoman_123 on Apr 26, 2012
Latest reply on Jul 17, 2015 by yiyuez

I have a large number of large ascii files and I need the centre values keep the same and the outer areas made NoData (outer values are water, inner values are land). I run the tool 'ASCII to Raster' then 'Extract by Mask' then convert back to ascii with Raster to ASCII.
When I use the Extract by Mask tool it works for the NoData task but the values in some inner cells change, similar yes, but have changed. Why does this tool change the values and how do you stop this?
I have tried many other ways to do the task, but can't even get close, it really doesn't seem like a complex task, it just won't work. Please help