pre_text: The following table shows the activity of our U.S. and international plan assets, which are measured at fair value using Level 3 inputs. (1) Balances as of December 31, 2018 have been revised from our 2018 Form 10-K filing to reflect changes in leveling classification of specific funds. These reclassifications did not impact the fair value of any of our pension plan assets. (2) Purchases of Level 3 assets in 2018 primarily represent the purchase of bulk annuity contracts (buy-ins) in some of our international plans.
table: December 31,
table: (In millions) 2019 2018
table: Balance at beginning of period(1) $ 150.1 $ 71.5
table: Gains (losses) on assets still held at end of year 16.8 (16.0)
table: Purchases, sales, issuance, and settlements(2) 8.3 103.7
table: Transfers in and/or out of Level 3 — 1.0
table: Foreign exchange gain (loss) 5.0 (10.1)
table: Balance at end of period(1) $ 180.2 $ 150.1
question: Analyse this data from a financial earnings document. What is the difference between the Balance at end of period for 2018 and 2019?