One of the things I miss from my old Ryobi BT3K was the accessory micro rip fence adjuster I had for it. This allowed very small accurate movements of the fence for sneaking up on a cut. It used a 16 TPI threaded rod and a knob with four increment lines around its circumference allowing for adjustments of 1/64". By interpolation, one could actually make adjustments of 1/128". That's just shy of 8 thousandths of an inch.
Needing to rout some sliding DTs to match the sockets I had cut previously, I re-remembered an old trick I had learned a while back. My router table is in one of the wings of my Griz Cabinet saw which has a Bessie type rip fence. While I used this method with the router table, it can also be used for the table saw and can likely be modified to other styles of rip fences also.
Okay, you have set the fence close, but proud of the cut you want to make and made the initial cut. Now you need to make an ever so miner adjustment to the fence to shave off a little more or what ever the case is. Trying to move that fence even as much as 1/16" easily becomes a comedy of errors, and accurately moving it less than that is outrageously impossible.
So, your fence is still locked down from the last process. You've determined the direction you need to move it and maybe even how much you need to move it. You need a block of scrap with a relatively straight edge on one surface. I used a little ~4" X 4" piece of MDF because it was handy. You also need a clamp with which to clamp the block to the rail for your fence. I used a 6" F-Style Pony bar clamp. You also need something to use as shims. I keep cut offs of thin pieces of stock from projects and sometimes even mark their thickness on them. This is handy if you know how much you need to move the fence. For the DTs I needed to be shaving mere thousandths off at each pass because I was test fitting after each pass and didn't want to over do it. So I used a scrap of copy paper, initially folded two times to make four thicknesses of paper. Place your shim next to the end of the appropriate leg of the T on your T-Square type fence, on top of the rail, then set the scrap block snugly against the shim, pushing it snugly against the edge of the leg of the fence and clamp it in place to the rail using your clamp. Now release the fence lock, remove your shim and slide the leg of the fence against the scrap block and lock the fence back down. You have moved your fence the thickness of the shim and are now ready to make your cut. In the case of the DTs I used the four thickness folded paper twice, then unfolded one fold to two thicknesses of the paper and finally one cut after moving the fence a single thickness of the paper with test fitting between each cut.
Since all five pairs of DT sockets had been made using a two stop method with my miter fence setup, all of them were of equal width and depth. By milling the sliding DTs by feeding the work between the fence and the router bit, the final width at the "neck" of the DTs were identical even if there were some variation in the thickness of the workpieces, so all of them could be cut once I had the final fit to the first one.
Other "shim" materials might include playing cards and for accurate known measurements, drill bits seem extremely right on the money.