diff --git a/docs/make.jl b/docs/make.jl
index e4e3f9f..d57419f 100644
--- a/docs/make.jl
+++ b/docs/make.jl
@@ -1,7 +1,7 @@
 using Documenter, GridVisualizeTools, ColorTypes
 
 function mkdocs()
-    DocMeta.setdocmeta!(GridVisualizeTools, :DocTestSetup, :(using GridVisualizeTools, ColorTypes); recursive=true)
+    DocMeta.setdocmeta!(GridVisualizeTools, :DocTestSetup, :(using GridVisualizeTools, ColorTypes, Colors); recursive=true)
     makedocs(sitename="GridVisualizeTools.jl",
              modules = [GridVisualizeTools],
              clean = false, 
diff --git a/docs/src/index.md b/docs/src/index.md
index 8e27af8..02e2667 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -12,6 +12,7 @@ $(read("../../README.md",String))
 region_cmap
 ```
 ```@example
+using GridVisualizeTools # hide
 region_cmap(5)
 ```
 
@@ -20,6 +21,7 @@ region_cmap(5)
 bregion_cmap
 ```
 ```@example
+using GridVisualizeTools # hide
 bregion_cmap(5)
 ```
 
@@ -66,13 +68,13 @@ marching_tetrahedra
 markerpoints
 ```
 
-## Makeplanes
+## Planes & isolevels
 ```@docs
 makeplanes
 ```
 
 ```jldoctest
-using GridVisualizeTools # hide
+using GridVisualizeTools
 makeplanes([0.,0,0], [1.,1,1], [0.5], [],[])
 # output
 1-element Vector{Vector{Float64}}:
@@ -80,10 +82,36 @@ makeplanes([0.,0,0], [1.,1,1], [0.5], [],[])
 ```
 
 ```jldoctest
-using GridVisualizeTools # hide
+using GridVisualizeTools
 makeplanes([0.,0,0], [1.,1,1], [0.5], [0.5],[])
 # output
 2-element Vector{Vector{Float64}}:
  [1.0, 0.0, 0.0, -0.5]
  [0.0, 1.0, 0.0, -0.5]
 ```
+
+
+```@docs
+makeisolevels
+```
+
+```jldoctest
+using GridVisualizeTools
+makeisolevels(0:0.1:10, 1, (-1,1),3)
+# output
+([-1.0, 0.0, 1.0], (-1, 1), [-1.0, 0.0, 1.0])
+```
+
+```jldoctest
+using GridVisualizeTools
+makeisolevels(0:0.1:10, 1, (1,-1),3)
+# output
+([0.0, 5.0, 10.0], (0.0, 10.0), [0.0, 5.0, 10.0])
+```
+
+```jldoctest
+using GridVisualizeTools
+makeisolevels(0:0.1:10, 1, (1,-1),nothing)
+# output
+([0.0, 5.0, 10.0], (0.0, 10.0), [0.0, 5.0, 10.0])
+```
diff --git a/src/GridVisualizeTools.jl b/src/GridVisualizeTools.jl
index 4a75dab..5442036 100644
--- a/src/GridVisualizeTools.jl
+++ b/src/GridVisualizeTools.jl
@@ -17,6 +17,6 @@ include("markerpoints.jl")
 export markerpoints
 
 include("planeslevels.jl")
-export makeplanes
+export makeplanes,makeisolevels
 
 end # module GridVisualizeTools
diff --git a/src/planeslevels.jl b/src/planeslevels.jl
index bef8768..661268c 100644
--- a/src/planeslevels.jl
+++ b/src/planeslevels.jl
@@ -40,3 +40,34 @@ function makeplanes(xyzmin,xyzmax,x,y,z)
     end
     planes
 end
+
+"""
+    $(SIGNATURES)
+
+Update levels, limits, colorbartics based on vector given in func.
+
+- if `limits[1]>limits[2]`, replace it by `extrema(func)`.
+- if levels is a number, replace it with a linear range in `limits` of length levels+2
+- if colorbarticks is `nothing` replace it with levels, otherwise, if it is a number, replace it
+  with a linear range of corresponding length
+"""
+function makeisolevels(func,levels,limits, colorbarticks)
+    
+    if limits[1]>limits[2] 
+        limits=extrema(func)
+    end
+    
+    if isa(levels,Number)
+        levels=collect(LinRange(limits[1],limits[2],levels+2))
+    end
+    
+    if colorbarticks == nothing
+        colorbarticks = levels
+    elseif isa(colorbarticks,Number)
+        colorbarticks = collect(limits[1]:(limits[2]-limits[1])/(colorbarticks-1):limits[2])
+    end
+    
+    #    map(t->round(t,sigdigits=4),levels),limits,map(t->round(t,sigdigits=4),colorbarticks)
+    levels,limits,colorbarticks
+
+end