Step 1th, open the Word2010 document window, click the formula you want to save to the formula Library to make it edit or select, and then click the Formula Options button and select the Save as New Formula command from the Open menu, as shown in Figure 2011072807.
Figure 2011072807 "Save as New formula" command
Step 2nd, open the New Building Block dialog box, enter the name of the formula in the Name box, leave the default settings for the other options, and click OK, as shown in Figure 2011072808.
Figure 2011072808 Word2010 New Building Block dialog box
Tip: A custom formula saved to the WORD2010 Formula Library is found in the formulas list in the formula Tools/design Ribbon Tools group. You can also save the new formula by selecting the Save selection to Formula Library command in the formula list, as shown in Figure 2011070809.
Figure 2011072809 using a custom formula in a formula library