Help with rpmfreqmap Error

I'm trying to create a Campbell, or waterfall plot for a rotating machinery problem.   I have been trying to use the rpmfreqmap function, but keep getting theser errors (pretty sure I have positive values):

Error using rpmfreqmap

Expected RPM to be positive.

Error in rpmmap>parseOptions (line 256)

validateattributes(rpm,{'numeric'},...

Error in rpmmap (line 12)

parseOptions(maptype,x,fs,rpm,varargin{:});

Error in rpmfreqmap (line 107)

[varargout{1:nargout}] = rpmmap(x,fs,rpm,'frequency',varargin{:});

Answer 1

[RichardB]

I'm going to answer my own question. The "RPM" needs to be positive as the error states. I modified the signal to be absolute which did not work. Turns out it does not like zeros either. So, I added a very small offset so that all "RPM" values were >0.