Heres a screen shot of what I've done so far. I also need table "products" to relate to table "estimate data".
The White Paper for FMP Novices is useful
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Looking at FMP business database demos is useful - some are fully useable
The Excelisys Business Tracker V3.0
Filemaker released a FMP runtime database in 2007 for students called "Campus Productivity Kit" and is available online, notably at CNet
Google "Campus Productivity Kit"
What is the difference between an estimate and an invoice?
Where I come from we have something like a "Price offer" and if the client accepts, you do the work, and the price offre becomes an invoice.
But the two are exactly the same, and the only difference is that an invoice get's an invoice number and needs to be payed.
You could just add a "Type" field to choose wether the Invoice is an invoice or an "Estimate". And you could print a different kind of document according to what Type you have.
Also I see You make an Estimate Id Match field in the Estimate Data table, but you relate it to the Customer ID Match field. That might not be a good Idea. It should be related to the EstimateId.
If you want to link to products you simply make a number field in the Estimates Data table called "ProductIdMatchField" and relate it to the products table.
It's possible that you need to make a second table occurence of the Products table but that's not a problem. In fact it's better, that way everything remains nice and organized. Just make a second table occurence and call it "ProductsEstimates".