the Garrard 301 plater is concaved.

The original Well Tempered platter was also concave, intentionally by design.

Most platters are slightly concave. Leveling them is easy as long as you align the level on a tangent to the outside edge. Of course you should be using a nice long level anyways!

I usually use both a long and a short I just got a new bubble and was trying it out. Didn't know the Garrard plater was concave always figured it was flat seems I was wrong haha. 

more funny then anything how we can make a simple mistake and have your whole set up off with out realising it. 

My early grease bearing 301 has a slightly concave platter too. I believe it is common. I believe it was made this way intentionally. If it bothers you, there are after-market platters on the market that offer slight benefits that may or may not be audible depending on the rest of your deck and system. Check out Peak HiFi in the UK. I bought Shaun's replacement brass bearing even though my original bearing looked brand new. I am a big believer in having the stoutest most precise main bearing possible. https://www.peakhifi.co.uk/cgi-bin/ecom.cgi?Command=ShowProduct&db_pid=718
https://www.peakhifi.co.uk/cgi-bin/ecom.cgi?Command=ShowProduct&db_pid=96

After noting the comments of the "slightly concave platter"
I proceeded to check my mid run 301 grease bearing 
and low and behold it is slightly concave.

There's always something to learn in this hobby. 

I believe it was made this way intentionally

I don't know if it was intentional, but I would think it's easier to make it flat, certainly if turned on a lathe. A slightly concave platter, used with a clamp, helps flatten the LP. 

The original platter was not turned on a lathe. It was cast and then spun balanced with drilling of the heavier spots. I wish the chassis was also cast-but it was stamped. There is lots of literature available on this. EW Mortimer's book on the history of Garrard is a good start. 

everything I ready prior to my posting said it was a design feature, I was just surprised to find it in a table designed in the 50's.  The old Garrard's were better designed then I originally thought, well at least included some modern thinking. 

My head is gong to explode. Google Art Dudley and Thorens and Garrard and read his essays. Don't believe Art Dudley, google Ken Shindo and Audio Note and Garrard. The Thorens TD124 and Garrard 301 were designed and built with a level of precision and craftsmanship and engineering that remains unmatched to the present day. Both were built to be used in the broadcast industry where it was common to run the decks 24/7 for months at a time. You apparently have a 301 so did you not do any research or listening comparisons before buying? Both do have their minor challenges. The TD124 platter sits low in the chassis and can create challenges getting a modern arm low enough. The Garrards require a plinth that is massive and arguably "tuned" to cancel out motor noise. 

Of course I read quite a bit about the Garrard tables and never came across anything about the plinth being concave. really I posted this for some of us that didn't know but also as a funny post of my set up mistake, as human we all do them from time to time. If you can not laugh at your self you've had a miserable life IMO. 

I built my Garrard set up over a year. Sort of fell into a one owner 301 late grease bearing table. When the original owner lost his vision he decided to sell his table to a good friend of mine who also owns a vintage audio shop.  I walked in one day asked him about Garrard's after reading a few reviews one was Art's build, I was considering building up a table. That's when he pulled out this one owner table that he had just picked up that day. It was in very good original owner and condition, owned and maintained by a meticulous machinist.  

So I bought it on the spot, $2000 for the table. A year later I was up and running with a custom Bamboo Plinth and Jelco 750L arm. I was coming from an Oracle Delphi mk4 and the improvement in many areas was immediate. I'm Happy with the results even if its still an ongoing project, adding a new arm board for a second arm and footer system. 

They are great tables and I get why people like them, even if its a bit of work in the end its worth it.