It keeps incrementing by larger and larger values even though we only want a single number incrementation.
Please post an example of the numbering method you want for your samples.
"single number incrementation" means what exactly"
Do you have a two part sample number such as?
1.1, 1.2, 1.3 for samples in group 1 and 2.1, 2.2, 2.3 for samples in group 2?
"Simply stated we would like file maker to auto enter the Sample ID number 1 larger than the previous largest ID number. "
This is the default behaviour for Filemaker when you select to auto-enter a serial number. It sets the next serial number to be 1 (you can make this auto-correct to be the next highest value) and to increment by 1 each time. Is this what you want? You can set that very simply in the Field Definition options. (In fact you would have to have gone to a wee bit of trouble to have un-set it.)