Raster calculater gives wrong result

[AntonKirillovichMalyshev]

Hi, I'm trying to calculate Canopy Height Model and values of result raster doesn't make sense. DSM (min value 203, max value 628 cell size x,y= 10) - DTM (min value 203, max value 596 cell size x,y= 10) = CHM (min -46 max 90 cell size x,y= 10). Any ideas how to fix it? 

[DavidPike]

Are the DSM and DTM from the same sensor and temporal resolution?  Check the areas of negative values to see if anything is obvious.  Also ensure a snap raster has been applied.

[AntonKirillovichMalyshev]

all settings seem correct, I tried to change the expression to sum (DSM+DTM) and it counts correctly, but with minus it's -46 and 90

[AntonKirillovichMalyshev · Accepted solution]

I found that the problem was caused by some high objects on DTM (some buildings became a part of the relief)