Data merge, multiple records. Master doc of grid element (text box with 1/2 width stroke) with number in corner. Excel csv file with header and numbers (a2 is "a1+1"). Merge and presto. You’ll need a big box to finish off the edges (still at 1/2 width). You’ll also need to plan your grid and Excel file, otherwise your grid will be incomplete (tho step and repeat will finish it off for you).