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Jimmy, If you don't specify the level of GRDNAM in gddiag, then the LEVEL1 and LEVEL2 of the resultant grid will be the first 2 levels in the equation (using gdinfo will show this). For example, your equation mul(omeg@500,vord) should result in a grid vorj@500:400 which is probably where you are running in to problems in the 3rd gfunc expression. You can work around this in 1 of 2 ways: 1) set the LEVEL1:LEVEL2 in the GRDNAM definition of the output grid gfunc = mul(omeg@500,vord) glevel = 400:600 grdnam = vord@400:600 2) rearrange the multiplication so that 400:600 are the first 2 levels gfunc = mul(vord,omeg@500) glevel = 400:600 grdnam = vord You can explicitly define all of the @, % and ^ inline definitions in the GRDNAM expression, so you could define a term as being valid on a different level- for instance if your result of the equation was surface vorticity using the sutpet terms, you could have grdnam=vor@0%none. Let me know if you have further questions. Steve Chiswell Unidata User Support On Thu, 29 Mar 2001, J. Correia wrote: > i am calculating terms in the vorticity tendency equation...enclosed is my > script... > my question is how to get the layer difference terms to carry over into > other calculations. i thought overspecifying would do it, but im just > missing something. the terms i have problems with are: > if ( $gfun == > 'quo(ldf(avor),200)' ) then > set glevel='400:600' > set grdnam='vord' > endif > if ( $gfun == 'mul(omeg@500,vord)' ) then > set glevel='400:600' > set grdnam='vorj' > endif > if ( $gfun == 'mul(-1,vorj)' ) then > set glevel='400:600' > set grdnam='vet2' > endif > the response i get is an error in the multiply command, even when i > specify the glevel to 500mb.... > any help would be much appreciated... > i havent seen anything in the help files, but i might be entering the > wrong key words.... > thanks again... > jimmyc > > >